[LeetCode] 225. 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 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).

// 3msclass MyStack {public:    /** Initialize your data structure here. */    MyStack() { }    /** Push element x onto stack. */    void push(int x) {        q.push(x);    }    /** Removes the element on top of the stack and returns that element. */    int pop() {        int rval = top();        for (int i = 0, n = q.size() - 1; i < n; i++) {            q.push(q.front());            q.pop();        }        q.pop();        return rval;    }    /** Get the top element. */    int top() {        return q.back();    }    /** Returns whether the stack is empty. */    bool empty() {        return q.empty();    }private:    queue<int> q;};