Implement Stack using Queues

mplement 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).

方法：队列实现栈，注意将数字压入到队列中时需要循环出队进队模拟栈，效率不高。

class MyStack {private:    queue<int> q;public:    /** Initialize your data structure here. */    MyStack() {    }    /** Push element x onto stack. */    void push(int x) {        q.push(x);        for(int i = 0 ; i < q.size() - 1; ++i){            q.push(q.front());            q.pop();        }    }    /** Removes the element on top of the stack and returns that element. */    int pop() {        int res = q.front();        q.pop();        return res;    }    /** Get the top element. */    int top() {        return q.front();     }    /** Returns whether the stack is empty. */    bool empty() {        return q.empty();    }};/** * 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(); * bool param_4 = obj.empty(); */