21、包含min函数的栈

没看懂要干啥的一道题？？？黑人问号？？？

import java.util.Stack;public class Solution {    Stack<Integer> stack = new Stack<>();    Stack<Integer> stack_min = new Stack<>();    public void push(int node) {        stack.push(node);        if(stack_min.isEmpty()){        stack_min.push(node);        }        else{        stack_min.push(Math.min(node, stack_min.peek()));        }    }        public void pop() {        stack.pop();        stack_min.pop();    }        public int top() {        return stack.peek();    }        public int min() {        return stack_min.peek();    }}