java相关-队列与栈-用队列实现栈-力扣225

package com.company;

import java.util.LinkedList;
import java.util.PriorityQueue;
import java.util.Queue;

public class MyStack {
    private Queue<Integer> queue;

    public MyStack() {
        queue = new LinkedList<>();
    }

    public void push(int x) {
        queue.add(x);

    }

    //把栈顶端的值弹出来
    public int pop() {
        rePosition();
        return queue.poll();
    }

    //获取栈顶端的值，但不弹出
    public int top() {
        rePosition();
        int result=queue.poll();
        queue.add(result);//原因是恢复队列刚装入数据的样子
        return result;
    }

    public boolean empty() {
        return queue.isEmpty();
    }
//改变位置
    public void rePosition(){
        int size = queue.size();
        size = size - 1;
        while (size > 0) {
            int value=queue.poll();//弹出
            queue.offer(value);
            size--;
        }
    }
}

package com.company;


import java.util.*;

public class Main {

    public static void main(String[] args) {

        MyStack stack=new MyStack();


        stack.push(1);
        stack.push(2);
        stack.push(3);
        System.out.println(stack.pop());//3
        System.out.println(stack.pop());//2
        System.out.println(stack.top());//1

    }





}