Implement Stack using Queues

Implementthe 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 mustuse only standard operations of a queue -- which means only push to back,peek/pop from front, size, and is empty operations are valid.
Dependingon your language, queue may not be supported natively. You may simulate a queueby using a list or deque (double-ended queue), as long as you use only standardoperations of a queue.
You mayassume that all operations are valid (for example, no pop or top operationswill be called on an empty stack).
 
除pop操作外，其他操作可以用queue的单步操作完成。
pop函数的思路如下：
假设queue中的元素是1 2 3 4，右边是头，左边是尾。要删除最左边的元素1。
将队列中除了队尾的元素依次弹出，然后加入到队尾。得到2 3 4 1。最后再将1弹出即可。

class Stack {
private:
queue<int> q;
public:
// Push element x onto stack.
void push(int x) {
q.push(x);
}

// Removes the element on top of the stack.
void pop() {
for(int i=0;i<q.size()-1;i++){
int n=q.front();
q.pop();
q.push(n);
}
q.pop();
}

// Get the top element.
int top() {
return q.back();
}

// Return whether the stack is empty.
bool empty() {
return q.empty();
}
};