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).

Update (2015-06-11):

The class name of the Java function had been updated to MyStack instead of Stack.

class Stack {
public:
queue<int> q;
// Push element x onto stack.
void push(int x) {
queue<int> tmp;
while(!q.empty()){
tmp.push(q.front());
q.pop();
}
q.push(x);
while(!tmp.empty()){
q.push(tmp.front());
tmp.pop();
}
}

// Removes the element on top of the stack.
void pop() {
q.pop();
}

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

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