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LC155_MinStack.java
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93 lines (77 loc) · 1.88 KB
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import java.util.ArrayList;
import java.util.NoSuchElementException;
/**
* Design a stack that supports push, pop, top, and retrieving the minimum element in constant
* time.
*
* push(x) -- Push element x onto stack. pop() -- Removes the element on top of the stack. top() --
* Get the top element. getMin() -- Retrieve the minimum element in the stack.
*
* Example:
* MinStack minStack = new MinStack();
* minStack.push(-2);
* minStack.push(0);
* minStack.push(-3);
* minStack.getMin(); --> Returns -3.
* minStack.pop();
* minStack.top(); --> Returns 0.
* minStack.getMin(); --> Returns -2.
*
* @authorLiu.3502
* @created2018-01-31 下午6:45
*/
public class LC155_MinStack{
public static void main(String[] args) {
}
//Wapper
class MinStackNode {
public Node ans;
public void push(int x) {
ans = ans == null ? new Node(x, x) : new Node(x, Math.min(x, ans.min), ans);
}
public void pop() {
ans = ans.next;
}
public int top() {
return ans.val;
}
public int getMin() {
return ans.min;
}
private class Node {
int val;
int min;
Node next;
private Node(int val, int min) {
this(val, min, null);
}
private Node(int val, int min, Node next) {
this.val = val;
this.min = min;
this.next = next;
}
}
}
//linklist
class MinStackList {
ArrayList<Integer> list;
public MinStackList() {
list = new ArrayList<Integer>();
}
public void push(int x) {
list.add(x);
}
public void pop() {
if (list.size() != 0) {
list.remove(list.size() - 1);
}
}
public int top() {
return list.get(list.size() - 1);
}
//Get Min element from stack
public int getMin() {
return list.stream().mapToInt(v -> v).min().orElseThrow(NoSuchElementException::new);
}
}
}