//兩個佇列：
class MyStack {

    Queue<Integer> queue1;
    Queue<Integer> queue2;
    public MyStack() {
        queue1 = new LinkedList<Integer>();//當作棧，隊頭當做棧頂
        queue2 = new LinkedList<Integer>();//輔助佇列，用來維持棧中元素，現有的順序
    }
    
    public void push(int x) {
        queue2.offer(x);
        while (!queue1.isEmpty()) {
            queue2.offer(queue1.poll());
        }
        Queue<Integer> temp = queue1;
        queue1 = queue2;
        queue2 = temp;
    }
    
    public int pop() {
        return queue1.poll();

    }
    
    public int top() {
        return queue1.peek();
    }
    
    public boolean empty() {
        return queue1.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();
 */
 

//一個佇列：
class MyStack {
    //佇列，可以維持元素的順序
    Queue<Integer> queue;//使用一個隊列當做棧，記錄在push之前元素的個數n，在push之後，依次取出該佇列中的n個元素，然後依次新增到佇列尾
    
    public MyStack() {
        queue = new LinkedList<Integer>();//當作棧，隊頭當做棧頂
    }
    
    public void push(int x) {
        int size = queue.size();
        queue.offer(x);
        for (int i = 0; i < size; i++) {
            queue.offer(queue.poll());
        }
    }
    
    public int pop() {
        return queue.poll();

    }
    
    public int top() {
        return queue.peek();
    }
    
    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();
 */