题解 | 包含min函数的栈

import java.util.*;
import java.util.Stack;

public class Solution {
    //用于栈的push和pop
    Stack<Integer> s1=new Stack<Integer>();
    //用于存储最小的min
    Stack<Integer> s2=new Stack<Integer>();
    
    public void push(int node) {
        s1.push(node);
        //空或者新元素较小时入栈
        if(s2.isEmpty()||s2.peek()>node)
            s2.push(node);
        else
            //重复加入栈顶 保持每次的最小元素
            s2.push(s2.peek());
    }
    
    public void pop() {
        s1.pop();
        s2.pop();        
    }
    
    public int top() {
        return s1.peek();
    }
    
    public int min() {
        return s2.peek();
    }
}