leetcode 225. Implement Stack using Queues

解题思路：
用队列的基本操作实现栈的基本操作

原题目：

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 only push to back, peek/pop from front, size, and is 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).

AC解，C++代码，菜鸟一个，请大家多多指正

class Stack {public:    queue<int> que;    // Push element x onto stack.    void push(int x) {        que.push(x);    }    // Removes the element on top of the stack.    void pop() {        queue<int> tmp_que;        while (que.size() != 1) {            int value = que.front();            que.pop();            tmp_que.push(value);        }        que = tmp_que;    }    // Get the top element.    int top() {        return que.back();    }    // Return whether the stack is empty.    bool empty() {        return que.empty();    }};