225. Implement 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 MyStack {

    Queue<Integer> q1 = new LinkedList<>();
    Queue<Integer> q2 = new LinkedList<>();

    // Push element x onto stack.
    public void push(int x) {
        q2.offer(x);
        while(!q1.isEmpty()){
            q2.offer(q1.poll());
        }
        Queue<Integer> q;
        q = q1;
        q1 = q2;
        q2 = q;
    }

    // Removes the element on top of the stack.
    public void pop() { 
        q1.poll();
    }

    // Get the top element.
    public int top() {
        return q1.peek();
    }

    // Return whether the stack is empty.
    public boolean empty() {
        return q1.isEmpty();
    }


}