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CountingSort.java
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97 lines (77 loc) · 3.1 KB
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package Sorts;
import java.util.*;
import java.util.stream.IntStream;
import java.util.stream.Stream;
import static java.util.stream.Collectors.toList;
import static java.util.stream.Collectors.toMap;
import static Sorts.SortUtils.print;
/**
* @author Youssef Ali (https://github.com/youssefAli11997)
* @author Podshivalov Nikita (https://github.com/nikitap492)
*/
class CountingSort implements SortAlgorithm {
@Override
public <T extends Comparable<T>> T[] sort(T[] unsorted) {
return sort(Arrays.asList(unsorted)).toArray(unsorted);
}
/**
* This method implements the Generic Counting Sort
*
* @param list The list to be sorted
* <p>
* Sorts the list in increasing order
* The method uses list elements as keys in the frequency map
**/
@Override
public <T extends Comparable<T>> List<T> sort(List<T> list) {
Map<T, Integer> frequency = new TreeMap<>();
// The final output array
List<T> sortedArray = new ArrayList<>(list.size());
// Counting the frequency of @param array elements
list.forEach(v -> frequency.put(v, frequency.getOrDefault(v, 0) + 1));
// Filling the sortedArray
for (Map.Entry<T, Integer> element : frequency.entrySet()) {
for (int j = 0; j < element.getValue(); j++) {
sortedArray.add(element.getKey());
}
}
return sortedArray;
}
/**
* Stream Counting Sort
* The same as method {@link CountingSort#sort(List)} } but this method uses stream API
*
* @param list The list to be sorted
**/
private static <T extends Comparable<T>> List<T> streamSort(List<T> list) {
return list.stream()
.collect(toMap(k -> k, v -> 1, (v1, v2) -> v1 + v2, TreeMap::new))
.entrySet()
.stream()
.flatMap(entry -> IntStream.rangeClosed(1, entry.getValue()).mapToObj(t -> entry.getKey()))
.collect(toList());
}
// Driver Program
public static void main(String[] args) {
// Integer Input
List<Integer> unsortedInts = Stream.of(4, 23, 6, 78, 1, 54, 23, 1, 9, 231, 9, 12).collect(toList());
CountingSort countingSort = new CountingSort();
System.out.println("Before Sorting:");
print(unsortedInts);
// Output => 1 1 4 6 9 9 12 23 23 54 78 231
System.out.println("After Sorting:");
print(countingSort.sort(unsortedInts));
System.out.println("After Sorting By Streams:");
print(streamSort(unsortedInts));
System.out.println("\n------------------------------\n");
// String Input
List<String> unsortedStrings = Stream.of("c", "a", "e", "b", "d", "a", "f", "g", "c").collect(toList());
System.out.println("Before Sorting:");
print(unsortedStrings);
//Output => a a b c c d e f g
System.out.println("After Sorting:");
print(countingSort.sort(unsortedStrings));
System.out.println("After Sorting By Streams:");
print(streamSort(unsortedStrings));
}
}