题解 | #包含min函数的栈#

思路：增加一个存放最小值的栈来实现（一开始理解错了题意，以为是用数组来实现栈的功能 orz）

import java.util.Stack;

public class Solution {

    Stack<Integer> s = new Stack<>();
    Stack<Integer> minNum = new Stack<>();
    //push()
    public void push(int node) {
        s.push(node);
        if(!minNum.empty()){
            if(node<=minNum.peek())minNum.push(node);
        }else{
            minNum.push(node);
        }
    }
    //pop()
    public void pop() {
        int a = s.pop();
        if(a==minNum.peek()){
            minNum.pop();
        }

    }
    //top()
    public int top() {
        return s.peek();
    }
    //min()
    public int min() {
        return minNum.peek();
    }
}