https://leetcode-cn.com/problems/implement-stack-using-queues/

题目描述

题解

• 使用一个队列实现即可
• 每次向队列中加入元素的时候，将队列中之前的元素全部出队列再入队列
• 这样最新入队列的元素，变成了第一个，第一个出队列。后入先出

class MyStack {Queue<Integer> queue = new LinkedList<Integer>();/** Initialize your data structure here. */public MyStack() {}/** Push element x onto stack. */public void push(int x) {int size = queue.size();queue.offer(x);// 将队列中原先存在的元素全部重新入一次队列for(int i=0; i<size; i++){queue.offer(queue.poll());}}/** Removes the element on top of the stack and returns that element. */public int pop() {return queue.poll();}/** Get the top element. */public int top() {return queue.peek();}/** Returns whether the stack is empty. */public boolean empty() {return queue.isEmpty();}
}/*** Your MyStack object will be instantiated and called as such:* MyStack obj = new MyStack();* obj.push(x);* int param_2 = obj.pop();* int param_3 = obj.top();* boolean param_4 = obj.empty();*/