Leetcode-Implement Stack using Queues（C++）

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).
题意：利用queue来设计一个stack，实现push，top，pop与empty
解题思路：关键在于保持新插入的数永远在queue的最前面。这样top以及pop的时候可以轻松操作。
建立两个queue，始终保持一个为空。
push：将插入值push入空的queue1，然后将另一个非空queue2中的数值依次弹出放入queue1.

class Stack {public:    queue<int> q[2];    int t=1;    // Push element x onto stack.    void push(int x) {        q[1-t].push(x);        while(!q[t].empty())        {            q[1-t].push(q[t].front());            q[t].pop();        }        t=1-t;//利用1-0=1和1-1=0来循环操作queue    }    // Removes the element on top of the stack.    void pop() {        if(!q[t].empty())        {            q[t].pop();        }    }    // Get the top element.    int top() {        if(!q[t].empty())        {            return q[t].front();        }    }    // Return whether the stack is empty.    bool empty() {        return q[t].empty();    }};