225. Implement Stack using Queues

class MyStack {
    //pop: pooll & offer elelments to the tail of the euque,
    // EXCEPT the last one
    // then pop the queue
    Queue<Integer> queue = new LinkedList<>();
    int topNum;
    /** Initialize your data structure here. */
    public MyStack() {
        
    }
    
    /** Push element x onto stack. */
    public void push(int x) {
        queue.offer(x);
        topNum=x;
    }
    
    /** Removes the element on top of the stack and returns that element. */
    public int pop() {
        int i=0;
        while(i++<queue.size()-1){
            if(i == queue.size()-1) topNum=queue.peek();
            queue.offer(queue.poll());
        }
        return queue.poll();
    }
    
    /** Get the top element. */
    public int top() {
        return topNum;
    }
    
    /** Returns whether the stack is empty. */
    public boolean empty() {
        return queue.isEmpty();
    }
}

/**
 * Your MyStack object will be instantiated and called as such:
 * MyStack obj = new MyStack();
 * obj.push(x);
 * int param_2 = obj.pop();
 * int param_3 = obj.top();
 * boolean param_4 = obj.empty();
 */