[LeetCode] Implement Stack using Queues

Problem:

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.

Java Code:

class MyStack {
    Queue<Integer> q1 = new LinkedList<Integer>();
    Queue<Integer> q2 = new LinkedList<Integer>();
    int size = 0;
    // Push element x onto stack.
    public void push(int x) {
        q1.add(x);
        size++;
    }

    // Removes the element on top of the stack.
    public void pop() {
        if (size == 0) {
            return;
        }
        int i = size;
        while (i != 1) {
            q2.add(q1.poll());
            i--;
        }
        size--;
        q1.poll();
        Queue<Integer> tempQ = q1;
        q1 = q2;
        q2 = tempQ;
        return;
    }

    // Get the top element.
    public int top() {
        if (size == 0) {
            return 0;
        }
        int i = size;
        while (i != 1) {
            q2.add(q1.poll());
            i--;
        }
        int tmp = q1.peek();
        q2.add(q1.poll());
        Queue<Integer> tempQ = q1;
        q1 = q2;
        q2 = tempQ;
        return tmp;
    }

    // Return whether the stack is empty.
    public boolean empty() {
        return (q1.peek() == null) && (q2.peek() == null);
    }
}