Min Stack

1 题目描述

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.

题目出处：https://leetcode.com/problems/min-stack/

2 源代码

package com.larry.easy;

import java.util.Stack;

public class MinStack {
private Stack<Integer> stack = new Stack<Integer>();
//因为时间复杂度要求是常数，则考虑加入一个栈来存储，最上面的元素为最小的元素
//这个题的关键是在minSta栈中的push()与pop()方法：入栈时判断，最小则压栈；出栈时判断，相等则出栈。
private Stack<Integer> minSta = new Stack<Integer>();

public void push(int x) {
stack.push(x);
if(minSta.empty() || x <= minSta.peek()) minSta.push(x);
}

public void pop() {
int temp = stack.pop();
if(temp == minSta.peek()) minSta.pop();
}

public int top() {
return stack.peek();
}

public int getMin() {
return minSta.peek();
}
}