225. 用队列实现栈

class MyStack {
    Queue<Integer> queue1;
    Queue<Integer> queue2;

    /** Initialize your data structure here. */
    public MyStack() {
        queue1=new LinkedList<Integer>();
        queue2=new LinkedList<Integer>();
    }
    
    /** Push element x onto stack. */
    public void push(int x) {
        queue2.offer(x);
        while(!queue1.isEmpty()){
            queue2.offer(queue1.remove());
        }
        //交换queue1 queue2
        Queue<Integer> temp=queue1;
        queue1=queue2;
        queue2=temp;
    }
    
    /** Removes the element on top of the stack and returns that element. */
    public int pop() {
        return queue1.remove();
    }
    
    /** Get the top element. */
    public int top() {
        return queue1.peek();
    }
    
    /** Returns whether the stack is empty. */
    public boolean empty() {
        return queue1.isEmpty();
    }
}