LeetCode-Implement Stack using Queues-解题报告

原题链接https://leetcode.com/problems/implement-stack-using-queues/

Implement the following operations of a stack using queues.

• push(x) -- Push element x onto stack.
• pop() -- Removes the element on top of the stack.
• top() -- Get the top element.
• empty() -- Return whether the stack is empty.

Notes:

• You must use only standard operations of a queue -- which means onlypush to back, peek/pop from front, size, andis empty operations are valid.
• Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
• You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

使用队列实现栈的功能。

使用两个队列mq,tmp

push：

当mq为空的时候，直接将元素x 压入mq

当mq部位空的时候，当队列中的元素循环取出压入临时队列tmp，在然后在将元素x压入mq，再将临时队列中的元素压入mq

pop：

弹出mq的第一个元素

top：

返回mq的的第一个元素

empty：

返回mq的empty情况

class Stack {public:    // Push element x onto stack.   // Push element x onto stack.queue<int>mq;queue<int>tmp;void push(int x) {if (mq.size() == 0){mq.push(x); return;}while (mq.size()){tmp.push(mq.front());mq.pop();}mq.push(x);while (tmp.size()){mq.push(tmp.front());tmp.pop();}}// Removes the element on top of the stack.void pop() {mq.pop();}// Get the top element.int top() {return mq.front();}// Return whether the stack is empty.bool empty() {return mq.empty();}};