225. Implement Stack using Queues

思路: 在add new item 之後將 除新item之後的數都加進queues中 e.g. 12--> 21 , add 3 --> 321 , add 4--> 4321

class MyStack {
    Queue queue;
    
    /** Initialize your data structure here. */
    public MyStack() {
        this.queue = new LinkedList<>();
    }
    
    /** Push element x onto stack. */
    public void push(int x) {
        queue.add(x);
        int size = queue.size();
        while(size>1){
            queue.add(queue.poll());
            size--;
        }
    }
    
    /** Removes the element on top of the stack and returns that element. */
    public int pop() {
        return queue.poll();
    }
    
    /** Get the top element. */
    public int top() {
        return queue.peek();
    }
    
    /** Returns whether the stack is empty. */
    public boolean empty() {
        return queue.isEmpty();
    }
}