maven-surefire-plugin
- 3.5.5
+ 3.5.6
@@ -82,7 +82,7 @@
org.jacoco
jacoco-maven-plugin
- 0.8.14
+ 0.8.15
@@ -112,7 +112,7 @@
com.puppycrawl.tools
checkstyle
- 13.4.2
+ 13.5.0
diff --git a/src/main/java/com/thealgorithms/audiofilters/EMAFilter.java b/src/main/java/com/thealgorithms/audiofilters/EMAFilter.java
index 0dd23e937953..4a9e954bd202 100644
--- a/src/main/java/com/thealgorithms/audiofilters/EMAFilter.java
+++ b/src/main/java/com/thealgorithms/audiofilters/EMAFilter.java
@@ -3,16 +3,19 @@
/**
* Exponential Moving Average (EMA) Filter for smoothing audio signals.
*
- * This filter applies an exponential moving average to a sequence of audio
+ *
+ * This filter applies an exponential moving average to a sequence of audio
* signal values, making it useful for smoothing out rapid fluctuations.
* The smoothing factor (alpha) controls the degree of smoothing.
*
- *
Based on the definition from
+ *
+ * Based on the definition from
* Wikipedia link.
*/
public class EMAFilter {
private final double alpha;
private double emaValue;
+
/**
* Constructs an EMA filter with a given smoothing factor.
*
@@ -26,14 +29,17 @@ public EMAFilter(double alpha) {
this.alpha = alpha;
this.emaValue = 0.0;
}
+
/**
* Applies the EMA filter to an audio signal array.
+ * EMA formula:
+ * EMA = alpha * currentSample + (1 - alpha) * previousEMA
*
* @param audioSignal Array of audio samples to process
* @return Array of processed (smoothed) samples
*/
public double[] apply(double[] audioSignal) {
- if (audioSignal.length == 0) {
+ if (audioSignal == null || audioSignal.length == 0) {
return new double[0];
}
double[] emaSignal = new double[audioSignal.length];
diff --git a/src/main/java/com/thealgorithms/backtracking/NQueens.java b/src/main/java/com/thealgorithms/backtracking/NQueens.java
index 1a8e453e34cb..404f677738a0 100644
--- a/src/main/java/com/thealgorithms/backtracking/NQueens.java
+++ b/src/main/java/com/thealgorithms/backtracking/NQueens.java
@@ -1,7 +1,9 @@
package com.thealgorithms.backtracking;
import java.util.ArrayList;
+import java.util.HashSet;
import java.util.List;
+import java.util.Set;
/**
* Problem statement: Given a N x N chess board. Return all arrangements in
@@ -32,7 +34,22 @@
* queen is not placed safely. If there is no such way then return an empty list
* as solution
*/
+
+/*
+ * Time Complexity: O(N!)
+ * space Complexity: O(N)
+ */
public final class NQueens {
+
+ // Store occupied rows for constant time safety check
+ private static final Set OCROWS = new HashSet<>();
+
+ // Store occupied main diagonals (row - column)
+ private static final Set OCDIAG = new HashSet<>();
+
+ // Store occupied anti-diagonals (row + columns)
+ private static final Set OCANTIDIAG = new HashSet<>();
+
private NQueens() {
}
@@ -43,10 +60,10 @@ public static List> getNQueensArrangements(int queens) {
}
public static void placeQueens(final int queens) {
- List> arrangements = new ArrayList>();
+ List> arrangements = new ArrayList<>();
getSolution(queens, arrangements, new int[queens], 0);
if (arrangements.isEmpty()) {
- System.out.println("There is no way to place " + queens + " queens on board of size " + queens + "x" + queens);
+ System.out.println(" no way to place " + queens + " queens on board of size " + queens + "x" + queens);
} else {
System.out.println("Arrangement for placing " + queens + " queens");
}
@@ -59,15 +76,15 @@ public static void placeQueens(final int queens) {
/**
* This is backtracking function which tries to place queen recursively
*
- * @param boardSize: size of chess board
- * @param solutions: this holds all possible arrangements
- * @param columns: columns[i] = rowId where queen is placed in ith column.
+ * @param boardSize: size of chess board
+ * @param solutions: this holds all possible arrangements
+ * @param columns: columns[i] = rowId where queen is placed in ith column.
* @param columnIndex: This is the column in which queen is being placed
*/
private static void getSolution(int boardSize, List> solutions, int[] columns, int columnIndex) {
if (columnIndex == boardSize) {
// this means that all queens have been placed
- List sol = new ArrayList();
+ List sol = new ArrayList<>();
for (int i = 0; i < boardSize; i++) {
StringBuilder sb = new StringBuilder();
for (int j = 0; j < boardSize; j++) {
@@ -82,30 +99,29 @@ private static void getSolution(int boardSize, List> solutions, int
// This loop tries to place queen in a row one by one
for (int rowIndex = 0; rowIndex < boardSize; rowIndex++) {
columns[columnIndex] = rowIndex;
- if (isPlacedCorrectly(columns, rowIndex, columnIndex)) {
- // If queen is placed successfully at rowIndex in column=columnIndex then try
- // placing queen in next column
- getSolution(boardSize, solutions, columns, columnIndex + 1);
- }
- }
- }
- /**
- * This function checks if queen can be placed at row = rowIndex in column =
- * columnIndex safely
- *
- * @param columns: columns[i] = rowId where queen is placed in ith column.
- * @param rowIndex: row in which queen has to be placed
- * @param columnIndex: column in which queen is being placed
- * @return true: if queen can be placed safely false: otherwise
- */
- private static boolean isPlacedCorrectly(int[] columns, int rowIndex, int columnIndex) {
- for (int i = 0; i < columnIndex; i++) {
- int diff = Math.abs(columns[i] - rowIndex);
- if (diff == 0 || columnIndex - i == diff) {
- return false;
+ // Skip current position if row or diagonal is already occupied
+ boolean isROp = OCROWS.contains(rowIndex);
+
+ boolean isDOp = OCDIAG.contains(rowIndex - columnIndex) || OCANTIDIAG.contains(rowIndex + columnIndex);
+
+ if (isROp || isDOp) {
+ continue;
}
+
+ // Mark current row and diagonal as occupied
+ OCROWS.add(rowIndex);
+ OCDIAG.add(rowIndex - columnIndex);
+ OCANTIDIAG.add(rowIndex + columnIndex);
+
+ // Move to the next column after placing current queen
+ getSolution(boardSize, solutions, columns, columnIndex + 1);
+
+ // Backtrack by removing current queen
+
+ OCROWS.remove(rowIndex);
+ OCDIAG.remove(rowIndex - columnIndex);
+ OCANTIDIAG.remove(rowIndex + columnIndex);
}
- return true;
}
}
diff --git a/src/main/java/com/thealgorithms/backtracking/RatInAMaze.java b/src/main/java/com/thealgorithms/backtracking/RatInAMaze.java
new file mode 100644
index 000000000000..183b4bbd97f8
--- /dev/null
+++ b/src/main/java/com/thealgorithms/backtracking/RatInAMaze.java
@@ -0,0 +1,119 @@
+package com.thealgorithms.backtracking;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * Rat in a Maze Problem using Backtracking.
+ *
+ * Given an {@code n x n} binary maze where {@code 1} represents an open cell
+ * and {@code 0} represents a blocked cell, find all paths for a rat starting at
+ * the top-left cell {@code (0, 0)} to reach the bottom-right cell {@code (n-1, n-1)}.
+ *
+ *
The rat can move in four directions: Up (U), Down (D), Left (L), Right (R).
+ * Each cell may be visited at most once per path.
+ *
+ *
Time Complexity: O(4^(n²)) in the worst case (four choices per cell).
+ * Space Complexity: O(n²) for the visited matrix and recursion stack.
+ *
+ *
Example:
+ *
+ * maze = { {1, 0, 0, 0},
+ * {1, 1, 0, 1},
+ * {0, 1, 0, 0},
+ * {0, 1, 1, 1} }
+ * Output: ["DDRDRR", "DRDDRR"] (two valid paths)
+ *
+ *
+ * @see Maze solving algorithm
+ * @author the-Sunny-Sharma (GitHub)
+ */
+public final class RatInAMaze {
+
+ private RatInAMaze() {
+ }
+
+ /**
+ * Finds all paths from the top-left to the bottom-right of the given maze.
+ *
+ * @param maze an {@code n x n} binary matrix where {@code 1} = open, {@code 0} = blocked
+ * @return a sorted list of all valid path strings using directions D, L, R, U;
+ * an empty list if no path exists
+ * @throws IllegalArgumentException if the maze is null, empty, or not square
+ */
+ public static List findPaths(final int[][] maze) {
+ if (maze == null || maze.length == 0) {
+ throw new IllegalArgumentException("Maze must not be null or empty.");
+ }
+ int n = maze.length;
+ for (int[] row : maze) {
+ if (row.length != n) {
+ throw new IllegalArgumentException("Maze must be a square (n x n) matrix.");
+ }
+ }
+ List results = new ArrayList<>();
+ if (maze[0][0] == 0 || maze[n - 1][n - 1] == 0) {
+ return results;
+ }
+ boolean[][] visited = new boolean[n][n];
+ solve(maze, 0, 0, n, "", visited, results);
+ return results;
+ }
+
+ /**
+ * Recursive backtracking helper that explores all four directions.
+ *
+ * @param maze the binary maze
+ * @param row current row position
+ * @param col current column position
+ * @param n maze dimension
+ * @param path path string built so far
+ * @param visited tracks visited cells for the current path
+ * @param results accumulates complete paths
+ */
+ private static void solve(final int[][] maze, final int row, final int col, final int n, final String path, final boolean[][] visited, final List results) {
+ // Base case: reached destination
+ if (row == n - 1 && col == n - 1) {
+ results.add(path);
+ return;
+ }
+
+ // Mark current cell as visited
+ visited[row][col] = true;
+
+ // Explore in alphabetical order: Down, Left, Right, Up
+ // Down
+ if (isSafe(maze, row + 1, col, n, visited)) {
+ solve(maze, row + 1, col, n, path + 'D', visited, results);
+ }
+ // Left
+ if (isSafe(maze, row, col - 1, n, visited)) {
+ solve(maze, row, col - 1, n, path + 'L', visited, results);
+ }
+ // Right
+ if (isSafe(maze, row, col + 1, n, visited)) {
+ solve(maze, row, col + 1, n, path + 'R', visited, results);
+ }
+ // Up
+ if (isSafe(maze, row - 1, col, n, visited)) {
+ solve(maze, row - 1, col, n, path + 'U', visited, results);
+ }
+
+ // Backtrack: unmark current cell
+ visited[row][col] = false;
+ }
+
+ /**
+ * Checks whether moving to {@code (row, col)} is valid.
+ *
+ * @param maze the binary maze
+ * @param row target row
+ * @param col target column
+ * @param n maze dimension
+ * @param visited tracks visited cells for the current path
+ * @return {@code true} if the cell is within bounds, open, and not yet visited
+ */
+ private static boolean isSafe(final int[][] maze, final int row, final int col, final int n, final boolean[][] visited) {
+ return row >= 0 && row < n && col >= 0 && col < n && maze[row][col] == 1 && !visited[row][col];
+ }
+}
diff --git a/src/main/java/com/thealgorithms/conversions/AnyBaseToAnyBase.java b/src/main/java/com/thealgorithms/conversions/AnyBaseToAnyBase.java
index 3d31cb3e7f6c..314e7fba38a3 100644
--- a/src/main/java/com/thealgorithms/conversions/AnyBaseToAnyBase.java
+++ b/src/main/java/com/thealgorithms/conversions/AnyBaseToAnyBase.java
@@ -1,10 +1,4 @@
-/**
- * [Brief description of what the algorithm does]
- *
- * Time Complexity: O(n) [or appropriate complexity]
- * Space Complexity: O(n)
- * @author Reshma Kakkirala
- */
+
package com.thealgorithms.conversions;
import java.util.Arrays;
diff --git a/src/main/java/com/thealgorithms/datastructures/queues/ThreadSafeQueue.java b/src/main/java/com/thealgorithms/datastructures/queues/ThreadSafeQueue.java
new file mode 100644
index 000000000000..a943b0028974
--- /dev/null
+++ b/src/main/java/com/thealgorithms/datastructures/queues/ThreadSafeQueue.java
@@ -0,0 +1,186 @@
+package com.thealgorithms.datastructures.queues;
+
+import java.util.concurrent.locks.Condition;
+import java.util.concurrent.locks.ReentrantLock;
+
+/**
+ * @brief Thread-safe bounded queue implementation using ReentrantLock and Condition variables
+ * @details A blocking queue that supports multiple producers and consumers.
+ * Uses a circular buffer internally with lock-based synchronization to ensure
+ * thread safety. Producers block when the queue is full, and consumers block
+ * when the queue is empty.
+ * @see Producer-Consumer Problem
+ */
+public class ThreadSafeQueue {
+
+ private final Object[] buffer;
+ private final int capacity;
+ private int head;
+ private int tail;
+ private int count;
+ private final ReentrantLock lock;
+ private final Condition notFull;
+ private final Condition notEmpty;
+
+ /**
+ * @brief Constructs a ThreadSafeQueue with the specified capacity
+ * @param capacity the maximum number of elements the queue can hold
+ * @throws IllegalArgumentException if capacity is less than or equal to zero
+ */
+ public ThreadSafeQueue(int capacity) {
+ if (capacity <= 0) {
+ throw new IllegalArgumentException("Capacity must be greater than zero.");
+ }
+ this.capacity = capacity;
+ this.buffer = new Object[capacity];
+ this.head = 0;
+ this.tail = 0;
+ this.count = 0;
+ this.lock = new ReentrantLock();
+ this.notFull = lock.newCondition();
+ this.notEmpty = lock.newCondition();
+ }
+
+ /**
+ * @brief Adds an element to the tail of the queue, blocking if full
+ * @param item the element to add
+ * @throws InterruptedException if the thread is interrupted while waiting
+ * @throws IllegalArgumentException if the item is null
+ */
+ public void enqueue(T item) throws InterruptedException {
+ if (item == null) {
+ throw new IllegalArgumentException("Cannot enqueue null item.");
+ }
+
+ lock.lock();
+ try {
+ while (count == capacity) {
+ notFull.await();
+ }
+ buffer[tail] = item;
+ tail = (tail + 1) % capacity;
+ count++;
+ notEmpty.signalAll();
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * @brief Removes and returns the element at the head of the queue, blocking if empty
+ * @return the element at the head of the queue
+ * @throws InterruptedException if the thread is interrupted while waiting
+ */
+ @SuppressWarnings("unchecked")
+ public T dequeue() throws InterruptedException {
+ lock.lock();
+ try {
+ while (count == 0) {
+ notEmpty.await();
+ }
+ T item = (T) buffer[head];
+ buffer[head] = null;
+ head = (head + 1) % capacity;
+ count--;
+ notFull.signalAll();
+ return item;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * @brief Adds an element to the tail of the queue without blocking
+ * @param item the element to add
+ * @return true if the element was added, false if the queue was full
+ * @throws IllegalArgumentException if the item is null
+ */
+ public boolean offer(T item) {
+ if (item == null) {
+ throw new IllegalArgumentException("Cannot enqueue null item.");
+ }
+
+ lock.lock();
+ try {
+ if (count == capacity) {
+ return false;
+ }
+ buffer[tail] = item;
+ tail = (tail + 1) % capacity;
+ count++;
+ notEmpty.signalAll();
+ return true;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * @brief Removes and returns the element at the head without blocking
+ * @return the element at the head, or null if the queue is empty
+ */
+ @SuppressWarnings("unchecked")
+ public T poll() {
+ lock.lock();
+ try {
+ if (count == 0) {
+ return null;
+ }
+ T item = (T) buffer[head];
+ buffer[head] = null;
+ head = (head + 1) % capacity;
+ count--;
+ notFull.signalAll();
+ return item;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * @brief Returns the number of elements in the queue
+ * @return the current size of the queue
+ */
+ public int size() {
+ lock.lock();
+ try {
+ return count;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * @brief Checks if the queue is empty
+ * @return true if the queue contains no elements
+ */
+ public boolean isEmpty() {
+ lock.lock();
+ try {
+ return count == 0;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * @brief Checks if the queue is full
+ * @return true if the queue has reached its capacity
+ */
+ public boolean isFull() {
+ lock.lock();
+ try {
+ return count == capacity;
+ } finally {
+ lock.unlock();
+ }
+ }
+
+ /**
+ * @brief Returns the maximum capacity of the queue
+ * @return the capacity
+ */
+ public int capacity() {
+ return capacity;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/datastructures/trees/WaveletTree.java b/src/main/java/com/thealgorithms/datastructures/trees/WaveletTree.java
new file mode 100644
index 000000000000..6feaa6f35048
--- /dev/null
+++ b/src/main/java/com/thealgorithms/datastructures/trees/WaveletTree.java
@@ -0,0 +1,235 @@
+package com.thealgorithms.datastructures.trees;
+
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * A Wavelet Tree is a highly efficient data structure used to store sequences
+ * and answer queries like rank, select, and quantile in O(log(max_val - min_val)) time.
+ * This structure is particularly useful in competitive programming and text compression.
+ */
+public class WaveletTree {
+
+ private class Node {
+ int low;
+ int high;
+ Node left;
+ Node right;
+ List leftCount; // Prefix sums of elements going to the left child
+
+ /**
+ * Recursively constructs the tree nodes by partitioning the array.
+ *
+ * @param arr the subarray for the current node
+ * @param low the minimum possible value in the current node
+ * @param high the maximum possible value in the current node
+ */
+ Node(int[] arr, int low, int high) {
+ this.low = low;
+ this.high = high;
+
+ if (low == high) {
+ return;
+ }
+
+ int mid = low + (high - low) / 2;
+ leftCount = new ArrayList<>(arr.length + 1);
+ leftCount.add(0);
+
+ List leftArr = new ArrayList<>();
+ List rightArr = new ArrayList<>();
+
+ for (int x : arr) {
+ if (x <= mid) {
+ leftArr.add(x);
+ leftCount.add(leftCount.get(leftCount.size() - 1) + 1);
+ } else {
+ rightArr.add(x);
+ leftCount.add(leftCount.get(leftCount.size() - 1));
+ }
+ }
+
+ if (!leftArr.isEmpty()) {
+ this.left = new Node(leftArr.stream().mapToInt(i -> i).toArray(), low, mid);
+ }
+ if (!rightArr.isEmpty()) {
+ this.right = new Node(rightArr.stream().mapToInt(i -> i).toArray(), mid + 1, high);
+ }
+ }
+ }
+
+ private Node root;
+ private final int n;
+
+ /**
+ * Constructs a Wavelet Tree from the given array.
+ * The min and max values are determined dynamically from the array.
+ *
+ * @param arr the input array
+ */
+ public WaveletTree(int[] arr) {
+ if (arr == null || arr.length == 0) {
+ this.n = 0;
+ return;
+ }
+ this.n = arr.length;
+ int min = arr[0];
+ int max = arr[0];
+ for (int x : arr) {
+ if (x < min) {
+ min = x;
+ }
+ if (x > max) {
+ max = x;
+ }
+ }
+ root = new Node(arr, min, max);
+ }
+
+ /**
+ * Constructs a Wavelet Tree from the given array with specific min and max values.
+ *
+ * @param arr the input array
+ * @param minValue the minimum possible value
+ * @param maxValue the maximum possible value
+ */
+ public WaveletTree(int[] arr, int minValue, int maxValue) {
+ if (arr == null || arr.length == 0) {
+ this.n = 0;
+ return;
+ }
+ this.n = arr.length;
+ root = new Node(arr, minValue, maxValue);
+ }
+
+ /**
+ * How many times does the number x appear in the array from index 0 to i (inclusive)?
+ *
+ * @param x the number to search for
+ * @param i the end index (0-based, inclusive)
+ * @return the number of occurrences of x in arr[0...i]
+ */
+ public int rank(int x, int i) {
+ if (root == null || x < root.low || x > root.high || i < 0) {
+ return 0;
+ }
+ // If i is out of bounds, cap it at n - 1
+ int endIdx = Math.min(i, n - 1);
+ return rank(root, x, endIdx + 1);
+ }
+
+ private int rank(Node node, int x, int count) {
+ if (node == null || count == 0) {
+ return 0;
+ }
+ if (node.low == node.high) {
+ return count;
+ }
+ int mid = node.low + (node.high - node.low) / 2;
+ int leftC = node.leftCount.get(count);
+ if (x <= mid) {
+ return rank(node.left, x, leftC);
+ } else {
+ return rank(node.right, x, count - leftC);
+ }
+ }
+
+ /**
+ * What is the 0-based index of the k-th occurrence of the number x in the array?
+ *
+ * @param x the number to search for
+ * @param k the occurrence count (1-based)
+ * @return the 0-based index in the original array, or -1 if x occurs less than k times
+ */
+ public int select(int x, int k) {
+ if (root == null || x < root.low || x > root.high || k <= 0) {
+ return -1;
+ }
+ if (rank(x, n - 1) < k) {
+ return -1;
+ }
+ return select(root, x, k);
+ }
+
+ private int select(Node node, int x, int k) {
+ if (node.low == node.high) {
+ return k - 1; // 0-based index within the imaginary array at the leaf
+ }
+ int mid = node.low + (node.high - node.low) / 2;
+ if (x <= mid) {
+ int posInLeft = select(node.left, x, k);
+ return binarySearchLeft(node.leftCount, posInLeft + 1);
+ } else {
+ int posInRight = select(node.right, x, k);
+ return binarySearchRight(node.leftCount, posInRight + 1);
+ }
+ }
+
+ private int binarySearchLeft(List prefixSums, int k) {
+ int l = 1;
+ int r = prefixSums.size() - 1;
+ int ans = -1;
+ while (l <= r) {
+ int mid = l + (r - l) / 2;
+ if (prefixSums.get(mid) >= k) {
+ ans = mid;
+ r = mid - 1;
+ } else {
+ l = mid + 1;
+ }
+ }
+ return ans == -1 ? -1 : ans - 1; // Convert to 0-based index
+ }
+
+ private int binarySearchRight(List prefixSums, int k) {
+ int l = 1;
+ int r = prefixSums.size() - 1;
+ int ans = -1;
+ while (l <= r) {
+ int mid = l + (r - l) / 2;
+ if (mid - prefixSums.get(mid) >= k) {
+ ans = mid;
+ r = mid - 1;
+ } else {
+ l = mid + 1;
+ }
+ }
+ return ans == -1 ? -1 : ans - 1; // Convert to 0-based index
+ }
+
+ /**
+ * If you sort the subarray from index left to right, what would be the k-th smallest element?
+ * This query is also commonly known as the quantile query.
+ *
+ * @param left the start index of the subarray (0-based, inclusive)
+ * @param right the end index of the subarray (0-based, inclusive)
+ * @param k the rank of the smallest element (1-based, e.g., k=1 is the minimum)
+ * @return the k-th smallest element in the subarray, or -1 if invalid parameters
+ */
+ public int kthSmallest(int left, int right, int k) {
+ if (root == null || left > right || left < 0 || k < 1 || k > right - left + 1) {
+ return -1;
+ }
+ return kthSmallest(root, left, right, k);
+ }
+
+ private int kthSmallest(Node node, int left, int right, int k) {
+ if (node.low == node.high) {
+ return node.low;
+ }
+
+ int countLeftInLMinus1 = (left == 0) ? 0 : node.leftCount.get(left);
+ int countLeftInR = node.leftCount.get(right + 1);
+ int elementsToLeft = countLeftInR - countLeftInLMinus1;
+
+ if (k <= elementsToLeft) {
+ int newL = countLeftInLMinus1;
+ int newR = countLeftInR - 1;
+ return kthSmallest(node.left, newL, newR, k);
+ } else {
+ int newL = left - countLeftInLMinus1;
+ int newR = right - countLeftInR;
+ return kthSmallest(node.right, newL, newR, k - elementsToLeft);
+ }
+ }
+}
diff --git a/src/main/java/com/thealgorithms/dynamicprogramming/DigitDP.java b/src/main/java/com/thealgorithms/dynamicprogramming/DigitDP.java
new file mode 100644
index 000000000000..7dae7603fedc
--- /dev/null
+++ b/src/main/java/com/thealgorithms/dynamicprogramming/DigitDP.java
@@ -0,0 +1,111 @@
+package com.thealgorithms.dynamicprogramming;
+import java.util.Arrays;
+
+/**
+ * A generalized template for the Digit Dynamic Programming (Digit DP)
+ * technique.
+ * Digit DP is used to count numbers within a range [L, R] that satisfy specific
+ * digit properties.
+ * This specific implementation demonstrates counting the numbers whose digit
+ * sum equals a target value.
+ *
+ *
+ * Example:
+ * countRangeWithDigitSum(1, 100, 5) returns 6 (numbers: 5, 14, 23, 32, 41, 50)
+ */
+public final class DigitDP {
+
+ // Maximum theoretical digit sum for a 64-bit signed long integer (9 * 19 digits
+ // = 171)
+ private static final int MAX_DIGIT_SUM = 171;
+
+ private DigitDP() {
+ // Prevent instantiation for utility/algorithm template class
+ }
+
+ /**
+ * Counts how many numbers in the range [L, R] have a digit sum equal to the
+ * target.
+ *
+ * @param l The lower bound of the range (inclusive).
+ * @param r The upper bound of the range (inclusive).
+ * @param target The exact sum of digits required.
+ * @return The count of valid integers.
+ */
+ public static long countRangeWithDigitSum(long l, long r, int target) {
+ if (l > r || target < 0 || target > MAX_DIGIT_SUM) {
+ return 0;
+ }
+ long countR = countWithDigitSum(r, target);
+ long countLMinus1 = countWithDigitSum(l - 1, target);
+ return countR - countLMinus1;
+ }
+
+ private static long countWithDigitSum(long number, int target) {
+ if (number < 0) {
+ return 0;
+ }
+ String numStr = Long.toString(number);
+ int length = numStr.length();
+
+ // dp[index][current_sum][tight]
+ long[][][] dp = new long[length][MAX_DIGIT_SUM + 1][2];
+ for (long[][] row : dp) {
+ for (long[] col : row) {
+ Arrays.fill(col, -1);
+ }
+ }
+
+ return solve(0, 0, 1, numStr, target, dp);
+ }
+
+ /**
+ * Recursive memoized function to explore digit placements.
+ *
+ * Time Complexity: O(number_of_digits * target_sum * 10)
+ * Space Complexity: O(number_of_digits * target_sum * 2)
+ *
+ * @param index Current digit position from left to right (most significant
+ * first).
+ * @param currentSum Cumulative sum of digits chosen so far.
+ * @param tight Flag indicating if current prefix matches the original
+ * number boundary.
+ * @param numStr String representation of the upper ceiling limit.
+ * @param target The exact required sum of digits.
+ * @param dp Memoization matrix cache table.
+ * @return Total valid combinations from the current state configuration.
+ */
+ private static long solve(int index, int currentSum, int tight, String numStr, int target, long[][][] dp) {
+ // Base case: If we have processed all digits
+ if (index == numStr.length()) {
+ return currentSum == target ? 1 : 0;
+ }
+
+ // Return memoized state if already evaluated
+ if (dp[index][currentSum][tight] != -1) {
+ return dp[index][currentSum][tight];
+ }
+
+ long ans = 0;
+ // Determine the maximum limit for the current position digit
+ int limit = (tight == 1) ? (numStr.charAt(index) - '0') : 9;
+
+ // Iterate through all possible valid digits for this position
+ for (int digit = 0; digit <= limit; digit++) {
+ int nextSum = currentSum + digit;
+
+ // Optimization: If the digit sum exceeds the target, prune branch
+ if (nextSum > target) {
+ continue;
+ }
+
+ // Next state remains tight only if current state is tight and we place the
+ // exact limit digit
+ int nextTight = (tight == 1 && digit == limit) ? 1 : 0;
+ ans += solve(index + 1, nextSum, nextTight, numStr, target, dp);
+ }
+
+ dp[index][currentSum][tight] = ans;
+ return ans;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/greedyalgorithms/CoinChange.java b/src/main/java/com/thealgorithms/greedyalgorithms/CoinChange.java
index 8054581d21d7..5f9f6080d0e1 100644
--- a/src/main/java/com/thealgorithms/greedyalgorithms/CoinChange.java
+++ b/src/main/java/com/thealgorithms/greedyalgorithms/CoinChange.java
@@ -6,10 +6,30 @@
// Problem Link : https://en.wikipedia.org/wiki/Change-making_problem
+/**
+ * The Coin Change problem finds the minimum number of coins needed
+ * to make a given amount using a greedy approach.
+ *
+ *
Note: This greedy approach works optimally for standard coin systems
+ * (like Indian currency), but may not work for all arbitrary coin sets.
+ * For arbitrary denominations, dynamic programming is preferred.
+ *
+ * @see Change-making problem
+ */
public final class CoinChange {
private CoinChange() {
}
- // Function to solve the coin change problem
+
+ /**
+ * Returns the list of coins used to make the given amount
+ * using a greedy algorithm with standard denominations.
+ *
+ *
Time Complexity: O(n log n) where n is the number of coin denominations
+ *
Space Complexity: O(n)
+ *
+ * @param amount the total amount to make change for
+ * @return list of coins used to make the amount
+ */
public static ArrayList coinChangeProblem(int amount) {
// Define an array of coin denominations in descending order
Integer[] coins = {1, 2, 5, 10, 20, 50, 100, 500, 2000};
diff --git a/src/main/java/com/thealgorithms/matrix/QRDecomposition.java b/src/main/java/com/thealgorithms/matrix/QRDecomposition.java
new file mode 100644
index 000000000000..45f56bc14729
--- /dev/null
+++ b/src/main/java/com/thealgorithms/matrix/QRDecomposition.java
@@ -0,0 +1,149 @@
+package com.thealgorithms.matrix;
+
+/**
+ * @brief Implementation of QR Decomposition using the Gram-Schmidt process
+ * @details Decomposes a matrix A into an orthogonal matrix Q and an upper
+ * triangular matrix R such that A = Q * R. The Gram-Schmidt process
+ * orthogonalizes the columns of A to produce Q, and R is computed as Q^T * A.
+ * This decomposition is useful for solving linear least squares problems,
+ * eigenvalue computations, and numerical stability in linear algebra.
+ * @see QR Decomposition
+ */
+public final class QRDecomposition {
+
+ private QRDecomposition() {
+ }
+
+ /**
+ * A helper class to store both Q and R matrices
+ */
+ public static class QR {
+ private final double[][] q;
+ private final double[][] r;
+
+ QR(double[][] q, double[][] r) {
+ this.q = q;
+ this.r = r;
+ }
+
+ public double[][] getQ() {
+ return q;
+ }
+
+ public double[][] getR() {
+ return r;
+ }
+ }
+
+ /**
+ * @brief Performs QR decomposition on a matrix using the Gram-Schmidt process
+ * @param matrix the input matrix (m x n)
+ * @return QR object containing orthogonal matrix Q (m x n) and upper triangular matrix R (n x n)
+ * @throws IllegalArgumentException if the matrix is null, empty, or has invalid rows
+ */
+ public static QR decompose(double[][] matrix) {
+ validateInputMatrix(matrix);
+
+ int m = matrix.length;
+ int n = matrix[0].length;
+
+ double[][] q = new double[m][n];
+ double[][] r = new double[n][n];
+
+ for (int j = 0; j < n; j++) {
+ double[] v = getColumn(matrix, j);
+
+ for (int i = 0; i < j; i++) {
+ double[] qi = getColumn(q, i);
+ r[i][j] = dotProduct(qi, v);
+ v = subtractVectors(v, scalarMultiply(qi, r[i][j]));
+ }
+
+ r[j][j] = norm(v);
+ if (r[j][j] == 0) {
+ throw new ArithmeticException("Matrix is rank deficient. Cannot perform QR decomposition.");
+ }
+ double[] qj = scalarMultiply(v, 1.0 / r[j][j]);
+ setColumn(q, j, qj);
+ }
+
+ return new QR(q, r);
+ }
+
+ private static double[] getColumn(double[][] matrix, int col) {
+ int m = matrix.length;
+ double[] column = new double[m];
+ for (int i = 0; i < m; i++) {
+ column[i] = matrix[i][col];
+ }
+ return column;
+ }
+
+ private static void setColumn(double[][] matrix, int col, double[] column) {
+ for (int i = 0; i < matrix.length; i++) {
+ matrix[i][col] = column[i];
+ }
+ }
+
+ private static double dotProduct(double[] a, double[] b) {
+ double sum = 0;
+ for (int i = 0; i < a.length; i++) {
+ sum += a[i] * b[i];
+ }
+ return sum;
+ }
+
+ private static double[] subtractVectors(double[] a, double[] b) {
+ double[] result = new double[a.length];
+ for (int i = 0; i < a.length; i++) {
+ result[i] = a[i] - b[i];
+ }
+ return result;
+ }
+
+ private static double[] scalarMultiply(double[] v, double scalar) {
+ double[] result = new double[v.length];
+ for (int i = 0; i < v.length; i++) {
+ result[i] = v[i] * scalar;
+ }
+ return result;
+ }
+
+ private static double norm(double[] v) {
+ return Math.sqrt(dotProduct(v, v));
+ }
+
+ private static void validateInputMatrix(double[][] matrix) {
+ if (matrix == null) {
+ throw new IllegalArgumentException("The input matrix cannot be null");
+ }
+ if (matrix.length == 0) {
+ throw new IllegalArgumentException("The input matrix cannot be empty");
+ }
+ if (!hasValidRows(matrix)) {
+ throw new IllegalArgumentException("The input matrix cannot have null or empty rows");
+ }
+ if (isJaggedMatrix(matrix)) {
+ throw new IllegalArgumentException("The input matrix cannot be jagged");
+ }
+ }
+
+ private static boolean hasValidRows(double[][] matrix) {
+ for (double[] row : matrix) {
+ if (row == null || row.length == 0) {
+ return false;
+ }
+ }
+ return true;
+ }
+
+ private static boolean isJaggedMatrix(double[][] matrix) {
+ int numColumns = matrix[0].length;
+ for (double[] row : matrix) {
+ if (row.length != numColumns) {
+ return true;
+ }
+ }
+ return false;
+ }
+}
diff --git a/src/main/java/com/thealgorithms/searches/InterpolationSearch.java b/src/main/java/com/thealgorithms/searches/InterpolationSearch.java
index d24cc1c774bc..272627fc48b4 100644
--- a/src/main/java/com/thealgorithms/searches/InterpolationSearch.java
+++ b/src/main/java/com/thealgorithms/searches/InterpolationSearch.java
@@ -1,14 +1,4 @@
-/**
- * Interpolation Search estimates the position of the target value
- * based on the distribution of values.
- *
- * Example:
- * Input: [10, 20, 30, 40], target = 30
- * Output: Index = 2
- *
- * Time Complexity: O(log log n) (average case)
- * Space Complexity: O(1)
- */
+
package com.thealgorithms.searches;
/**
diff --git a/src/main/java/com/thealgorithms/searches/LinearSearch.java b/src/main/java/com/thealgorithms/searches/LinearSearch.java
index 3f273e167f0a..c5f6e6ba9776 100644
--- a/src/main/java/com/thealgorithms/searches/LinearSearch.java
+++ b/src/main/java/com/thealgorithms/searches/LinearSearch.java
@@ -1,16 +1,4 @@
-/**
- * Performs Linear Search on an array.
- *
- * Linear search checks each element one by one until the target is found
- * or the array ends.
- *
- * Example:
- * Input: [2, 4, 6, 8], target = 6
- * Output: Index = 2
- *
- * Time Complexity: O(n)
- * Space Complexity: O(1)
- */
+
package com.thealgorithms.searches;
import com.thealgorithms.devutils.searches.SearchAlgorithm;
@@ -22,10 +10,34 @@
*
* It works for both sorted and unsorted arrays.
*
+ * How it works step-by-step:
+ *
+ * - Start from the first element of the array.
+ * - Compare the current element with the target value.
+ * - If they match, return the current index.
+ * - If they don't match, move to the next element.
+ * - Repeat until the element is found or the array ends.
+ * - If not found, return -1.
+ *
+ *
+ * Example:
+ *
+ * Input array: [5, 3, 8, 1, 9]
+ * Target: 8
+ *
+ * Step 1: Compare 5 with 8 → no match, move on
+ * Step 2: Compare 3 with 8 → no match, move on
+ * Step 3: Compare 8 with 8 → match found at index 2!
+ *
+ * Output: 2
+ *
+ * If target = 7:
+ * Output: -1 (not found)
+ *
* Time Complexity:
- * - Best case: O(1)
- * - Average case: O(n)
- * - Worst case: O(n)
+ * - Best case: O(1) - target is the first element
+ * - Average case: O(n) - target is somewhere in the middle
+ * - Worst case: O(n) - target is last or not present
*
* Space Complexity: O(1)
*
@@ -37,9 +49,10 @@
public class LinearSearch implements SearchAlgorithm {
/**
- * Generic Linear search method
+ * Generic Linear search method that searches for a value
+ * in the given array by checking each element one by one.
*
- * @param array List to be searched
+ * @param array List to be searched (can be unsorted)
* @param value Key being searched for
* @return Location of the key, -1 if array is null or empty, or key not found
*/
diff --git a/src/main/java/com/thealgorithms/strings/AlternativeStringArrange.java b/src/main/java/com/thealgorithms/strings/AlternativeStringArrange.java
index cf736dbd8cab..016ee2821a17 100644
--- a/src/main/java/com/thealgorithms/strings/AlternativeStringArrange.java
+++ b/src/main/java/com/thealgorithms/strings/AlternativeStringArrange.java
@@ -21,12 +21,19 @@ private AlternativeStringArrange() {
/**
* Arranges two strings by alternating their characters.
+ * If one string is longer than the other, the remaining characters of the longer string
+ * are appended at the end of the result.
*
- * @param firstString the first input string
- * @param secondString the second input string
+ * @param firstString the first input string, must not be {@code null}
+ * @param secondString the second input string, must not be {@code null}
* @return a new string with characters from both strings arranged alternately
+ * @throws IllegalArgumentException if {@code firstString} or {@code secondString} is {@code null}
*/
public static String arrange(String firstString, String secondString) {
+ if (firstString == null || secondString == null) {
+ throw new IllegalArgumentException("Input strings must not be null");
+ }
+
StringBuilder result = new StringBuilder();
int length1 = firstString.length();
int length2 = secondString.length();
diff --git a/src/test/java/com/thealgorithms/backtracking/RatInAMazeTest.java b/src/test/java/com/thealgorithms/backtracking/RatInAMazeTest.java
new file mode 100644
index 000000000000..ecd1f3c4dfae
--- /dev/null
+++ b/src/test/java/com/thealgorithms/backtracking/RatInAMazeTest.java
@@ -0,0 +1,99 @@
+package com.thealgorithms.backtracking;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+import static org.junit.jupiter.api.Assertions.assertTrue;
+
+import java.util.List;
+import org.junit.jupiter.api.Test;
+
+class RatInAMazeTest {
+
+ @Test
+ void testMultiplePathsExist() {
+ int[][] maze = {{1, 0, 0, 0}, {1, 1, 0, 1}, {0, 1, 0, 0}, {0, 1, 1, 1}};
+
+ List paths = RatInAMaze.findPaths(maze);
+ assertTrue(paths.size() >= 1);
+ for (String path : paths) {
+ assertTrue(path.chars().allMatch(c -> "DLRU".indexOf(c) >= 0));
+ }
+ }
+
+ @Test
+ void testSinglePath() {
+ int[][] maze = {{1, 0, 0}, {1, 1, 0}, {0, 1, 1}};
+ List paths = RatInAMaze.findPaths(maze);
+ assertEquals(1, paths.size());
+ assertEquals("DRDR", paths.get(0));
+ }
+
+ @Test
+ void testNoPathExists() {
+ int[][] maze = {{1, 0, 0}, {0, 0, 0}, {0, 0, 1}};
+ List paths = RatInAMaze.findPaths(maze);
+ assertTrue(paths.isEmpty());
+ }
+
+ @Test
+ void testSourceBlocked() {
+ int[][] maze = {{0, 1}, {1, 1}};
+ List paths = RatInAMaze.findPaths(maze);
+ assertTrue(paths.isEmpty());
+ }
+
+ @Test
+ void testDestinationBlocked() {
+ int[][] maze = {{1, 1}, {1, 0}};
+ List paths = RatInAMaze.findPaths(maze);
+ assertTrue(paths.isEmpty());
+ }
+
+ @Test
+ void testSingleCellMazeOpen() {
+ int[][] maze = {{1}};
+ List paths = RatInAMaze.findPaths(maze);
+ assertEquals(1, paths.size());
+ assertEquals("", paths.get(0));
+ }
+
+ @Test
+ void testSingleCellMazeBlocked() {
+ int[][] maze = {{0}};
+ List paths = RatInAMaze.findPaths(maze);
+ assertTrue(paths.isEmpty());
+ }
+
+ @Test
+ void testNullMazeThrowsException() {
+ assertThrows(IllegalArgumentException.class, () -> RatInAMaze.findPaths(null));
+ }
+
+ @Test
+ void testEmptyMazeThrowsException() {
+ assertThrows(IllegalArgumentException.class, () -> RatInAMaze.findPaths(new int[][] {}));
+ }
+
+ @Test
+ void testNonSquareMazeThrowsException() {
+ int[][] maze = {{1, 0, 1}, {1, 1, 1}};
+ assertThrows(IllegalArgumentException.class, () -> RatInAMaze.findPaths(maze));
+ }
+
+ @Test
+ void testAllCellsOpen() {
+ int[][] maze = {{1, 1, 1}, {1, 1, 1}, {1, 1, 1}};
+ List paths = RatInAMaze.findPaths(maze);
+ assertTrue(paths.size() > 1);
+ }
+
+ @Test
+ void testLargerMazeWithPath() {
+ int[][] maze = {{1, 1, 1, 1}, {0, 1, 0, 1}, {0, 1, 0, 1}, {0, 1, 1, 1}};
+ List paths = RatInAMaze.findPaths(maze);
+ assertTrue(paths.size() >= 1);
+ for (String path : paths) {
+ assertTrue(path.chars().allMatch(c -> "DLRU".indexOf(c) >= 0), "Path contains invalid characters: " + path);
+ }
+ }
+}
diff --git a/src/test/java/com/thealgorithms/datastructures/bag/BagTest.java b/src/test/java/com/thealgorithms/datastructures/bag/BagTest.java
index 8212793dfb79..f85a4628a1ac 100644
--- a/src/test/java/com/thealgorithms/datastructures/bag/BagTest.java
+++ b/src/test/java/com/thealgorithms/datastructures/bag/BagTest.java
@@ -98,11 +98,9 @@ void testIterator() {
@Test
void testIteratorEmptyBag() {
Bag bag = new Bag<>();
- int count = 0;
- for (String ignored : bag) {
- org.junit.jupiter.api.Assertions.fail("Iterator should not return any items for an empty bag");
+ for (String item : bag) {
+ org.junit.jupiter.api.Assertions.fail("Iterator returned item for an empty bag:" + item);
}
- assertEquals(0, count, "Iterator should not traverse any items in an empty bag");
}
@Test
diff --git a/src/test/java/com/thealgorithms/datastructures/lists/MergeSortedArrayListTest.java b/src/test/java/com/thealgorithms/datastructures/lists/MergeSortedArrayListTest.java
index 5483bbcd0394..4390c0f5f2eb 100644
--- a/src/test/java/com/thealgorithms/datastructures/lists/MergeSortedArrayListTest.java
+++ b/src/test/java/com/thealgorithms/datastructures/lists/MergeSortedArrayListTest.java
@@ -2,98 +2,51 @@
import static org.junit.jupiter.api.Assertions.assertEquals;
import static org.junit.jupiter.api.Assertions.assertThrows;
-import static org.junit.jupiter.api.Assertions.assertTrue;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
+import java.util.stream.Stream;
import org.junit.jupiter.api.Test;
+import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
+import org.junit.jupiter.params.provider.MethodSource;
class MergeSortedArrayListTest {
- @Test
- void testMergeTwoSortedLists() {
- List listA = Arrays.asList(1, 3, 5, 7, 9);
- List listB = Arrays.asList(2, 4, 6, 8, 10);
+ @ParameterizedTest(name = "{3}")
+ @MethodSource("provideMergeTestData")
+ void testMergeParameterizedScenarios(List listA, List listB, List expected, String scenarioName) {
List result = new ArrayList<>();
-
MergeSortedArrayList.merge(listA, listB, result);
-
- List expected = Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10);
- assertEquals(expected, result, "Merged list should be sorted and contain all elements from both input lists.");
+ assertEquals(expected, result, () -> "Failed scenario: " + scenarioName);
}
- @Test
- void testMergeWithEmptyList() {
- List listA = Arrays.asList(1, 2, 3);
- List listB = new ArrayList<>(); // Empty list
- List result = new ArrayList<>();
-
- MergeSortedArrayList.merge(listA, listB, result);
-
- List expected = Arrays.asList(1, 2, 3);
- assertEquals(expected, result, "Merged list should match listA when listB is empty.");
- }
-
- @Test
- void testMergeWithBothEmptyLists() {
- List listA = new ArrayList<>(); // Empty list
- List listB = new ArrayList<>(); // Empty list
- List result = new ArrayList<>();
-
- MergeSortedArrayList.merge(listA, listB, result);
-
- assertTrue(result.isEmpty(), "Merged list should be empty when both input lists are empty.");
+ private static Stream provideMergeTestData() {
+ return Stream.of(Arguments.of(Arrays.asList(1, 3, 5, 7, 9), Arrays.asList(2, 4, 6, 8, 10), Arrays.asList(1, 2, 3, 4, 5, 6, 7, 8, 9, 10), "Standard alternating sorted lists"), Arguments.of(Arrays.asList(1, 2, 3), new ArrayList<>(), Arrays.asList(1, 2, 3), "Merge with empty second list"),
+ Arguments.of(new ArrayList<>(), Arrays.asList(4, 5, 6), Arrays.asList(4, 5, 6), "Merge with empty first list"), Arguments.of(new ArrayList<>(), new ArrayList<>(), new ArrayList<>(), "Merge with both lists empty"),
+ Arguments.of(Arrays.asList(1, 2, 2, 3), Arrays.asList(2, 3, 4), Arrays.asList(1, 2, 2, 2, 3, 3, 4), "Handling duplicate elements gracefully"),
+ Arguments.of(Arrays.asList(-3, -1, 2), Arrays.asList(-2, 0, 3), Arrays.asList(-3, -2, -1, 0, 2, 3), "Handling negative numbers mixed with positive numbers"));
}
@Test
- void testMergeWithDuplicateElements() {
- List listA = Arrays.asList(1, 2, 2, 3);
- List listB = Arrays.asList(2, 3, 4);
+ void testMergeThrowsExceptionWhenListAIsNull() {
+ List listB = Arrays.asList(1, 2, 3);
List result = new ArrayList<>();
-
- MergeSortedArrayList.merge(listA, listB, result);
-
- List expected = Arrays.asList(1, 2, 2, 2, 3, 3, 4);
- assertEquals(expected, result, "Merged list should correctly handle and include duplicate elements.");
+ assertThrows(NullPointerException.class, () -> MergeSortedArrayList.merge(null, listB, result));
}
@Test
- void testMergeWithNegativeAndPositiveNumbers() {
- List listA = Arrays.asList(-3, -1, 2);
- List listB = Arrays.asList(-2, 0, 3);
+ void testMergeThrowsExceptionWhenListBIsNull() {
+ List listA = Arrays.asList(1, 2, 3);
List result = new ArrayList<>();
-
- MergeSortedArrayList.merge(listA, listB, result);
-
- List expected = Arrays.asList(-3, -2, -1, 0, 2, 3);
- assertEquals(expected, result, "Merged list should correctly handle negative and positive numbers.");
+ assertThrows(NullPointerException.class, () -> MergeSortedArrayList.merge(listA, null, result));
}
@Test
- void testMergeThrowsExceptionOnNullInput() {
- List listA = null;
- List listB = Arrays.asList(1, 2, 3);
- List result = new ArrayList<>();
-
- List finalListB = listB;
- List finalListA = listA;
- List finalResult = result;
- assertThrows(NullPointerException.class, () -> MergeSortedArrayList.merge(finalListA, finalListB, finalResult), "Should throw NullPointerException if any input list is null.");
-
- listA = Arrays.asList(1, 2, 3);
- listB = null;
- List finalListA1 = listA;
- List finalListB1 = listB;
- List finalResult1 = result;
- assertThrows(NullPointerException.class, () -> MergeSortedArrayList.merge(finalListA1, finalListB1, finalResult1), "Should throw NullPointerException if any input list is null.");
-
- listA = Arrays.asList(1, 2, 3);
- listB = Arrays.asList(4, 5, 6);
- result = null;
- List finalListA2 = listA;
- List finalListB2 = listB;
- List finalResult2 = result;
- assertThrows(NullPointerException.class, () -> MergeSortedArrayList.merge(finalListA2, finalListB2, finalResult2), "Should throw NullPointerException if the result collection is null.");
+ void testMergeThrowsExceptionWhenResultCollectionIsNull() {
+ List listA = Arrays.asList(1, 2, 3);
+ List listB = Arrays.asList(4, 5, 6);
+ assertThrows(NullPointerException.class, () -> MergeSortedArrayList.merge(listA, listB, null));
}
}
diff --git a/src/test/java/com/thealgorithms/datastructures/queues/ThreadSafeQueueTest.java b/src/test/java/com/thealgorithms/datastructures/queues/ThreadSafeQueueTest.java
new file mode 100644
index 000000000000..4c038c05b167
--- /dev/null
+++ b/src/test/java/com/thealgorithms/datastructures/queues/ThreadSafeQueueTest.java
@@ -0,0 +1,295 @@
+package com.thealgorithms.datastructures.queues;
+
+import java.util.ArrayList;
+import java.util.List;
+import java.util.concurrent.CountDownLatch;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.Executors;
+import java.util.concurrent.TimeUnit;
+import java.util.concurrent.atomic.AtomicInteger;
+import org.junit.jupiter.api.Assertions;
+import org.junit.jupiter.api.Test;
+
+public class ThreadSafeQueueTest {
+
+ @Test
+ public void testEnqueueDequeue() throws InterruptedException {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(5);
+ queue.enqueue(1);
+ queue.enqueue(2);
+ queue.enqueue(3);
+
+ Assertions.assertEquals(3, queue.size());
+ Assertions.assertEquals(1, queue.dequeue());
+ Assertions.assertEquals(2, queue.dequeue());
+ Assertions.assertEquals(3, queue.dequeue());
+ Assertions.assertTrue(queue.isEmpty());
+ }
+
+ @Test
+ public void testOfferPoll() {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(2);
+ Assertions.assertTrue(queue.offer("a"));
+ Assertions.assertTrue(queue.offer("b"));
+ Assertions.assertFalse(queue.offer("c"));
+
+ Assertions.assertEquals("a", queue.poll());
+ Assertions.assertEquals("b", queue.poll());
+ Assertions.assertNull(queue.poll());
+ }
+
+ @Test
+ public void testOfferRejectsWhenFull() {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(2);
+ Assertions.assertTrue(queue.offer(1));
+ Assertions.assertTrue(queue.offer(2));
+ Assertions.assertFalse(queue.offer(3));
+ Assertions.assertEquals(2, queue.size());
+ }
+
+ @Test
+ public void testPollReturnsNullWhenEmpty() {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(5);
+ Assertions.assertNull(queue.poll());
+ }
+
+ @Test
+ public void testEnqueueNullThrows() {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(5);
+ Assertions.assertThrows(IllegalArgumentException.class, () -> queue.enqueue(null));
+ }
+
+ @Test
+ public void testOfferNullThrows() {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(5);
+ Assertions.assertThrows(IllegalArgumentException.class, () -> queue.offer(null));
+ }
+
+ @Test
+ public void testInvalidCapacityThrows() {
+ Assertions.assertThrows(IllegalArgumentException.class, () -> new ThreadSafeQueue<>(0));
+ Assertions.assertThrows(IllegalArgumentException.class, () -> new ThreadSafeQueue<>(-1));
+ }
+
+ @Test
+ public void testIsEmptyAndIsFull() throws InterruptedException {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(2);
+ Assertions.assertTrue(queue.isEmpty());
+ Assertions.assertFalse(queue.isFull());
+
+ queue.enqueue(1);
+ Assertions.assertFalse(queue.isEmpty());
+ Assertions.assertFalse(queue.isFull());
+
+ queue.enqueue(2);
+ Assertions.assertFalse(queue.isEmpty());
+ Assertions.assertTrue(queue.isFull());
+
+ queue.dequeue();
+ Assertions.assertFalse(queue.isEmpty());
+ Assertions.assertFalse(queue.isFull());
+
+ queue.dequeue();
+ Assertions.assertTrue(queue.isEmpty());
+ Assertions.assertFalse(queue.isFull());
+ }
+
+ @Test
+ public void testCapacity() {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(10);
+ Assertions.assertEquals(10, queue.capacity());
+ }
+
+ @Test
+ public void testCircularBufferWrapAround() throws InterruptedException {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(3);
+ queue.enqueue(1);
+ queue.enqueue(2);
+ queue.enqueue(3);
+
+ Assertions.assertEquals(1, queue.dequeue());
+ Assertions.assertEquals(2, queue.dequeue());
+
+ queue.enqueue(4);
+ queue.enqueue(5);
+
+ Assertions.assertEquals(3, queue.dequeue());
+ Assertions.assertEquals(4, queue.dequeue());
+ Assertions.assertEquals(5, queue.dequeue());
+ }
+
+ @Test
+ public void testMultipleProducersSingleConsumer() throws InterruptedException {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(100);
+ int numProducers = 4;
+ int itemsPerProducer = 250;
+ int totalItems = numProducers * itemsPerProducer;
+ CountDownLatch doneLatch = new CountDownLatch(numProducers);
+ List results = new ArrayList<>();
+
+ ExecutorService executor = Executors.newFixedThreadPool(numProducers + 1);
+
+ for (int p = 0; p < numProducers; p++) {
+ final int producerId = p;
+ executor.submit(() -> {
+ try {
+ for (int i = 0; i < itemsPerProducer; i++) {
+ queue.enqueue(producerId * itemsPerProducer + i);
+ }
+ } catch (InterruptedException e) {
+ Thread.currentThread().interrupt();
+ } finally {
+ doneLatch.countDown();
+ }
+ });
+ }
+
+ Thread consumerThread = new Thread(() -> {
+ try {
+ while (results.size() < totalItems) {
+ Integer item = queue.poll();
+ if (item != null) {
+ synchronized (results) {
+ results.add(item);
+ }
+ }
+ }
+ } catch (Exception e) {
+ Thread.currentThread().interrupt();
+ }
+ });
+ consumerThread.start();
+
+ Assertions.assertTrue(doneLatch.await(10, TimeUnit.SECONDS));
+ consumerThread.join(5000);
+
+ Assertions.assertEquals(totalItems, results.size());
+ executor.shutdown();
+ Assertions.assertTrue(executor.awaitTermination(5, TimeUnit.SECONDS));
+ }
+
+ @Test
+ public void testSingleProducerMultipleConsumers() throws InterruptedException {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(50);
+ int numConsumers = 4;
+ int totalItems = 1000;
+ CountDownLatch doneLatch = new CountDownLatch(numConsumers);
+ AtomicInteger consumedCount = new AtomicInteger(0);
+
+ ExecutorService executor = Executors.newFixedThreadPool(numConsumers + 1);
+
+ executor.submit(() -> {
+ try {
+ for (int i = 0; i < totalItems; i++) {
+ queue.enqueue(i);
+ }
+ } catch (InterruptedException e) {
+ Thread.currentThread().interrupt();
+ }
+ });
+
+ for (int c = 0; c < numConsumers; c++) {
+ executor.submit(() -> {
+ try {
+ while (consumedCount.get() < totalItems) {
+ Integer item = queue.poll();
+ if (item != null) {
+ consumedCount.incrementAndGet();
+ }
+ }
+ } finally {
+ doneLatch.countDown();
+ }
+ });
+ }
+
+ Assertions.assertTrue(doneLatch.await(10, TimeUnit.SECONDS));
+ Assertions.assertEquals(totalItems, consumedCount.get());
+ executor.shutdown();
+ Assertions.assertTrue(executor.awaitTermination(5, TimeUnit.SECONDS));
+ }
+
+ @Test
+ public void testBlockingEnqueueWhenFull() throws InterruptedException {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(1);
+ queue.enqueue(1);
+
+ AtomicInteger blockedCount = new AtomicInteger(0);
+ Thread producer = new Thread(() -> {
+ try {
+ queue.enqueue(2);
+ blockedCount.incrementAndGet();
+ } catch (InterruptedException e) {
+ Thread.currentThread().interrupt();
+ }
+ });
+ producer.start();
+
+ Thread.sleep(100);
+ Assertions.assertEquals(1, queue.dequeue());
+
+ producer.join(2000);
+ Assertions.assertEquals(1, blockedCount.get());
+ Assertions.assertEquals(2, queue.dequeue());
+ }
+
+ @Test
+ public void testBlockingDequeueWhenEmpty() throws InterruptedException {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(5);
+
+ AtomicInteger result = new AtomicInteger(-1);
+ Thread consumer = new Thread(() -> {
+ try {
+ result.set(queue.dequeue());
+ } catch (InterruptedException e) {
+ Thread.currentThread().interrupt();
+ }
+ });
+ consumer.start();
+
+ Thread.sleep(100);
+ queue.enqueue(42);
+
+ consumer.join(2000);
+ Assertions.assertEquals(42, result.get());
+ }
+
+ @Test
+ public void testStressConcurrentAccess() throws InterruptedException {
+ ThreadSafeQueue queue = new ThreadSafeQueue<>(10);
+ int numThreads = 8;
+ int opsPerThread = 500;
+ CountDownLatch latch = new CountDownLatch(numThreads);
+ AtomicInteger enqueueCount = new AtomicInteger(0);
+ AtomicInteger dequeueCount = new AtomicInteger(0);
+
+ ExecutorService executor = Executors.newFixedThreadPool(numThreads);
+
+ for (int t = 0; t < numThreads; t++) {
+ final boolean isProducer = t % 2 == 0;
+ executor.submit(() -> {
+ try {
+ for (int i = 0; i < opsPerThread; i++) {
+ if (isProducer) {
+ if (queue.offer(i)) {
+ enqueueCount.incrementAndGet();
+ }
+ } else {
+ if (queue.poll() != null) {
+ dequeueCount.incrementAndGet();
+ }
+ }
+ }
+ } finally {
+ latch.countDown();
+ }
+ });
+ }
+
+ Assertions.assertTrue(latch.await(10, TimeUnit.SECONDS));
+ Assertions.assertTrue(enqueueCount.get() >= dequeueCount.get());
+ Assertions.assertEquals(enqueueCount.get() - dequeueCount.get(), queue.size());
+ executor.shutdown();
+ executor.awaitTermination(5, TimeUnit.SECONDS);
+ }
+}
diff --git a/src/test/java/com/thealgorithms/datastructures/trees/WaveletTreeTest.java b/src/test/java/com/thealgorithms/datastructures/trees/WaveletTreeTest.java
new file mode 100644
index 000000000000..592170673a3a
--- /dev/null
+++ b/src/test/java/com/thealgorithms/datastructures/trees/WaveletTreeTest.java
@@ -0,0 +1,117 @@
+package com.thealgorithms.datastructures.trees;
+
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+public class WaveletTreeTest {
+
+ @Test
+ public void testRank() {
+ int[] arr = {5, 1, 2, 5, 1};
+ WaveletTree wt = new WaveletTree(arr);
+
+ // x = 1
+ assertEquals(1, wt.rank(1, 1)); // In [5, 1], '1' appears 1 time
+ assertEquals(2, wt.rank(1, 4)); // In [5, 1, 2, 5, 1], '1' appears 2 times
+ assertEquals(0, wt.rank(1, 0)); // In [5], '1' appears 0 times
+
+ // x = 5
+ assertEquals(1, wt.rank(5, 0)); // In [5], '5' appears 1 time
+ assertEquals(1, wt.rank(5, 2)); // In [5, 1, 2], '5' appears 1 time
+ assertEquals(2, wt.rank(5, 4)); // In [5, 1, 2, 5, 1], '5' appears 2 times
+
+ // Out of bounds / invalid value
+ assertEquals(0, wt.rank(10, 4)); // '10' is not in the array
+ assertEquals(0, wt.rank(5, -1)); // Invalid end index
+ }
+
+ @Test
+ public void testSelect() {
+ int[] arr = {5, 1, 2, 5, 1};
+ WaveletTree wt = new WaveletTree(arr);
+
+ assertEquals(1, wt.select(1, 1)); // 1st '1' is at index 1
+ assertEquals(4, wt.select(1, 2)); // 2nd '1' is at index 4
+
+ assertEquals(0, wt.select(5, 1)); // 1st '5' is at index 0
+ assertEquals(3, wt.select(5, 2)); // 2nd '5' is at index 3
+
+ assertEquals(2, wt.select(2, 1)); // 1st '2' is at index 2
+
+ assertEquals(-1, wt.select(5, 3)); // 3rd '5' doesn't exist
+ assertEquals(-1, wt.select(10, 1)); // '10' doesn't exist
+ assertEquals(-1, wt.select(5, 0)); // invalid k
+ }
+
+ @Test
+ public void testKthSmallest() {
+ int[] arr = {5, 1, 2, 5, 1};
+ WaveletTree wt = new WaveletTree(arr);
+
+ // Array: [5, 1, 2, 5, 1] -> Sorted: [1, 1, 2, 5, 5]
+ assertEquals(1, wt.kthSmallest(0, 4, 1)); // 1st smallest in [5, 1, 2, 5, 1] is 1
+ assertEquals(1, wt.kthSmallest(0, 4, 2)); // 2nd smallest in [5, 1, 2, 5, 1] is 1
+ assertEquals(2, wt.kthSmallest(0, 4, 3)); // 3rd smallest in [5, 1, 2, 5, 1] is 2
+ assertEquals(5, wt.kthSmallest(0, 4, 4)); // 4th smallest in [5, 1, 2, 5, 1] is 5
+ assertEquals(5, wt.kthSmallest(0, 4, 5)); // 5th smallest in [5, 1, 2, 5, 1] is 5
+
+ // Subarray: arr[1..3] = [1, 2, 5] -> Sorted: [1, 2, 5]
+ assertEquals(1, wt.kthSmallest(1, 3, 1)); // 1st smallest in [1, 2, 5] is 1
+ assertEquals(2, wt.kthSmallest(1, 3, 2)); // 2nd smallest in [1, 2, 5] is 2
+ assertEquals(5, wt.kthSmallest(1, 3, 3)); // 3rd smallest in [1, 2, 5] is 5
+
+ // Invalid ranges / arguments
+ assertEquals(-1, wt.kthSmallest(4, 2, 1)); // Invalid range (left > right)
+ assertEquals(-1, wt.kthSmallest(0, 4, 10)); // k > range length
+ assertEquals(-1, wt.kthSmallest(0, 4, 0)); // k < 1
+ }
+
+ @Test
+ public void testEmptyAndSingleElementArray() {
+ WaveletTree wtEmpty = new WaveletTree(new int[] {});
+ assertEquals(0, wtEmpty.rank(1, 0));
+ assertEquals(-1, wtEmpty.select(1, 1));
+ assertEquals(-1, wtEmpty.kthSmallest(0, 0, 1));
+
+ WaveletTree wtSingle = new WaveletTree(new int[] {42});
+ assertEquals(1, wtSingle.rank(42, 0));
+ assertEquals(0, wtSingle.rank(42, -1));
+ assertEquals(0, wtSingle.select(42, 1));
+ assertEquals(-1, wtSingle.select(42, 2));
+ assertEquals(42, wtSingle.kthSmallest(0, 0, 1));
+ }
+
+ @Test
+ public void testNullArrayAndCustomBounds() {
+ WaveletTree wtNull = new WaveletTree(null);
+ assertEquals(0, wtNull.rank(1, 0));
+
+ WaveletTree wtNullCustom = new WaveletTree(null, 1, 5);
+ assertEquals(-1, wtNullCustom.select(1, 1));
+
+ int[] arr = {5, 1, 2, 5, 1};
+ WaveletTree wtCustom = new WaveletTree(arr, 1, 10);
+ assertEquals(2, wtCustom.rank(5, 4));
+ assertEquals(0, wtCustom.rank(4, 4)); // Query an element inside bounds but not in array
+ assertEquals(0, wtCustom.rank(10, 4)); // Query upper bound
+ }
+
+ @Test
+ public void testNegativeValues() {
+ int[] arr = {-5, 10, -2, 0, -5};
+ WaveletTree wt = new WaveletTree(arr);
+
+ assertEquals(2, wt.rank(-5, 4));
+ assertEquals(1, wt.rank(0, 3));
+
+ assertEquals(0, wt.select(-5, 1));
+ assertEquals(4, wt.select(-5, 2));
+ assertEquals(3, wt.select(0, 1));
+
+ // Sorted: [-5, -5, -2, 0, 10]
+ assertEquals(-5, wt.kthSmallest(0, 4, 1));
+ assertEquals(-2, wt.kthSmallest(0, 4, 3));
+ assertEquals(10, wt.kthSmallest(0, 4, 5));
+ }
+}
diff --git a/src/test/java/com/thealgorithms/dynamicprogramming/DigitDPTest.java b/src/test/java/com/thealgorithms/dynamicprogramming/DigitDPTest.java
new file mode 100644
index 000000000000..762fe86d4d65
--- /dev/null
+++ b/src/test/java/com/thealgorithms/dynamicprogramming/DigitDPTest.java
@@ -0,0 +1,70 @@
+package com.thealgorithms.dynamicprogramming;
+import static org.junit.jupiter.api.Assertions.assertEquals;
+
+import org.junit.jupiter.api.Test;
+
+/**
+ * Unit tests for the generalized DigitDP implementation.
+ */
+public class DigitDPTest {
+
+ @Test
+ public void testDigitDPBasicRange() {
+ // Numbers between 1 and 20 with a digit sum of 5: 5, 14
+ long result = DigitDP.countRangeWithDigitSum(1, 20, 5);
+ assertEquals(2, result);
+ }
+
+ @Test
+ public void testDigitDPZeroBound() {
+ // Number 0 has a digit sum of 0
+ long result = DigitDP.countRangeWithDigitSum(0, 0, 0);
+ assertEquals(1, result);
+ }
+
+ @Test
+ public void testDigitDPLargeRange() {
+ // Count numbers between 1 and 100 with a digit sum of 9
+ // 9, 18, 27, 36, 45, 54, 63, 72, 81, 90 (10 numbers)
+ long result = DigitDP.countRangeWithDigitSum(1, 100, 9);
+ assertEquals(10, result);
+ }
+
+ @Test
+ public void testDigitDPNoMatches() {
+ // No numbers between 10 and 15 can have a digit sum of 20
+ long result = DigitDP.countRangeWithDigitSum(10, 15, 20);
+ assertEquals(0, result);
+ }
+
+ @Test
+ public void testDigitDPExceedsMaxSum() {
+ // Sum condition that exceeds max possible physical sum array constraints
+ // gracefully returns 0
+ long result = DigitDP.countRangeWithDigitSum(1, 100, 200);
+ assertEquals(0, result);
+ }
+
+ @Test
+ public void testDigitDPInvalidRange() {
+ // Lower bound greater than upper bound should evaluate gracefully to 0
+ long result = DigitDP.countRangeWithDigitSum(50, 20, 5);
+ assertEquals(0, result);
+ }
+
+ @Test
+ public void testDigitDPExceedsMaxSumEdgeCase() {
+ // Yeh test case target > MAX_DIGIT_SUM wali condition ko hit karega
+ long result = DigitDP.countRangeWithDigitSum(1, 100, 180);
+ assertEquals(0, result);
+ }
+
+ @Test
+ public void testDigitDPMemoizationHit() {
+ // Badi range dene se overlapping subproblems bante hain,
+ // jisse memoization hit hogi aur coverage 100% ho jayegi.
+ long result1 = DigitDP.countRangeWithDigitSum(1, 100000, 15);
+ long result2 = DigitDP.countRangeWithDigitSum(1, 100000, 15);
+ assertEquals(result1, result2);
+ }
+}
diff --git a/src/test/java/com/thealgorithms/matrix/QRDecompositionTest.java b/src/test/java/com/thealgorithms/matrix/QRDecompositionTest.java
new file mode 100644
index 000000000000..adc8fb717e57
--- /dev/null
+++ b/src/test/java/com/thealgorithms/matrix/QRDecompositionTest.java
@@ -0,0 +1,115 @@
+package com.thealgorithms.matrix;
+
+import static org.junit.jupiter.api.Assertions.assertArrayEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
+
+import org.junit.jupiter.api.Test;
+
+public class QRDecompositionTest {
+
+ private static final double DELTA = 1e-9;
+
+ @Test
+ public void testQRDecomposition2x2() {
+ double[][] matrix = {{12, -51}, {6, 167}};
+ QRDecomposition.QR qr = QRDecomposition.decompose(matrix);
+ double[][] q = qr.getQ();
+ double[][] r = qr.getR();
+
+ double[][] reconstructed = multiplyMatrices(q, r);
+ for (int i = 0; i < matrix.length; i++) {
+ assertArrayEquals(matrix[i], reconstructed[i], DELTA);
+ }
+ }
+
+ @Test
+ public void testQRDecomposition3x3() {
+ double[][] matrix = {{1, 1, 0}, {1, 0, 1}, {0, 1, 1}};
+ QRDecomposition.QR qr = QRDecomposition.decompose(matrix);
+ double[][] q = qr.getQ();
+ double[][] r = qr.getR();
+
+ double[][] reconstructed = multiplyMatrices(q, r);
+ for (int i = 0; i < matrix.length; i++) {
+ assertArrayEquals(matrix[i], reconstructed[i], DELTA);
+ }
+ }
+
+ @Test
+ public void testQROrthogonalColumns() {
+ double[][] matrix = {{1, 1, 0}, {1, 0, 1}, {0, 1, 1}};
+ QRDecomposition.QR qr = QRDecomposition.decompose(matrix);
+ double[][] q = qr.getQ();
+
+ for (int i = 0; i < q[0].length; i++) {
+ for (int j = i; j < q[0].length; j++) {
+ double dot = 0;
+ for (int k = 0; k < q.length; k++) {
+ dot += q[k][i] * q[k][j];
+ }
+ if (i == j) {
+ assertArrayEquals(new double[] {1.0}, new double[] {dot}, DELTA);
+ } else {
+ assertArrayEquals(new double[] {0.0}, new double[] {dot}, DELTA);
+ }
+ }
+ }
+ }
+
+ @Test
+ public void testRIsUpperTriangular() {
+ double[][] matrix = {{12, -51}, {6, 167}};
+ QRDecomposition.QR qr = QRDecomposition.decompose(matrix);
+ double[][] r = qr.getR();
+
+ for (int i = 1; i < r.length; i++) {
+ for (int j = 0; j < i; j++) {
+ assertArrayEquals(new double[] {0.0}, new double[] {r[i][j]}, DELTA);
+ }
+ }
+ }
+
+ @Test
+ public void testQRDecompositionIdentityMatrix() {
+ double[][] matrix = {{1, 0, 0}, {0, 1, 0}, {0, 0, 1}};
+ QRDecomposition.QR qr = QRDecomposition.decompose(matrix);
+ double[][] q = qr.getQ();
+ double[][] r = qr.getR();
+
+ for (int i = 0; i < matrix.length; i++) {
+ assertArrayEquals(matrix[i], q[i], DELTA);
+ assertArrayEquals(matrix[i], r[i], DELTA);
+ }
+ }
+
+ @Test
+ public void testQRDecompositionRankDeficientThrows() {
+ double[][] matrix = {{1, 2}, {2, 4}};
+ assertThrows(ArithmeticException.class, () -> QRDecomposition.decompose(matrix));
+ }
+
+ @Test
+ public void testQRDecompositionNullMatrixThrows() {
+ assertThrows(IllegalArgumentException.class, () -> QRDecomposition.decompose(null));
+ }
+
+ @Test
+ public void testQRDecompositionEmptyMatrixThrows() {
+ assertThrows(IllegalArgumentException.class, () -> QRDecomposition.decompose(new double[0][0]));
+ }
+
+ private static double[][] multiplyMatrices(double[][] a, double[][] b) {
+ int m = a.length;
+ int n = b[0].length;
+ int k = a[0].length;
+ double[][] result = new double[m][n];
+ for (int i = 0; i < m; i++) {
+ for (int j = 0; j < n; j++) {
+ for (int p = 0; p < k; p++) {
+ result[i][j] += a[i][p] * b[p][j];
+ }
+ }
+ }
+ return result;
+ }
+}
diff --git a/src/test/java/com/thealgorithms/strings/AlternativeStringArrangeTest.java b/src/test/java/com/thealgorithms/strings/AlternativeStringArrangeTest.java
index 9e8ae9e9f153..4cd55a4d7410 100644
--- a/src/test/java/com/thealgorithms/strings/AlternativeStringArrangeTest.java
+++ b/src/test/java/com/thealgorithms/strings/AlternativeStringArrangeTest.java
@@ -1,9 +1,11 @@
package com.thealgorithms.strings;
import static org.junit.jupiter.api.Assertions.assertEquals;
+import static org.junit.jupiter.api.Assertions.assertThrows;
import java.util.stream.Stream;
import org.junit.jupiter.params.ParameterizedTest;
+import org.junit.jupiter.params.provider.Arguments;
import org.junit.jupiter.params.provider.MethodSource;
class AlternativeStringArrangeTest {
@@ -20,4 +22,15 @@ private static Stream provideTestData() {
void arrangeTest(String input1, String input2, String expected) {
assertEquals(expected, AlternativeStringArrange.arrange(input1, input2));
}
+
+ @ParameterizedTest(name = "null input ({0}, {1}) should throw IllegalArgumentException")
+ @MethodSource("provideNullInputs")
+ void arrangeThrowsOnNullInput(String input1, String input2) {
+ IllegalArgumentException ex = assertThrows(IllegalArgumentException.class, () -> AlternativeStringArrange.arrange(input1, input2));
+ assertEquals("Input strings must not be null", ex.getMessage());
+ }
+
+ private static Stream provideNullInputs() {
+ return Stream.of(Arguments.of(null, "abc"), Arguments.of("abc", null), Arguments.of(null, null));
+ }
}