1. 题目

使用栈实现队列的下列操作：

push(x) – 将一个元素放入队列的尾部。
pop() – 从队列首部移除元素。
peek() – 返回队列首部的元素。
empty() – 返回队列是否为空。

来源：力扣（LeetCode）
链接：https://leetcode-cn.com/problems/implement-queue-using-stacks
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类似题目LeetCode 225. 用队列实现栈

2. 解题

class MyQueue {stack<int> inSTK;stack<int> outSTK;
public:/** Initialize your data structure here. */MyQueue() { }    /** Push element x to the back of queue. */void push(int x) {inSTK.push(x);}/** Removes the element from in front of queue and returns that element. */int pop() {if(!outSTK.empty()){int tp = outSTK.top();outSTK.pop();return tp;}else{while(!inSTK.empty()){outSTK.push(inSTK.top());inSTK.pop();}int tp = outSTK.top();outSTK.pop();return tp;}}/** Get the front element. */int peek() {if(!outSTK.empty())return outSTK.top();else{while(!inSTK.empty()){outSTK.push(inSTK.top());inSTK.pop();}return outSTK.top();}}/** Returns whether the queue is empty. */bool empty() {return inSTK.empty() && outSTK.empty();}
};