题解 | #包含min函数的栈#双栈实现（时间复杂度o(1)） 也可以双list实现 思路一样

import java.util.Stack;

public class Solution {

    private Stack<Integer> stack = new Stack<>();
    private Stack<Integer> minStack = new Stack<>();
    public void push(int node) {
        stack.push(node);
        if(minStack.isEmpty()){
            minStack.push(node);
        } else {
            int top = minStack.peek();
            minStack.push(Math.min(top,node));
        }
    }

    public void pop() {
        if(!stack.isEmpty()){
            stack.pop();
            minStack.pop();
        }
    }

    public int top() {
        if(!stack.isEmpty()){
            return stack.peek();
        } else {
            return -1;
        }
    }

    public int min() {
        if(!minStack.isEmpty()){
            return minStack.peek();
        } else {
            return -1;
        }
    }
}