[leetcode]Implement Stack using Queues

题目如下：

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.
Notes:
You must use only standard operations of a queue – which means only push to back, peek/pop from front, size, and is empty operations are valid.
Depending on your language, queue may not be supported natively. You may simulate a queue by using a list or deque (double-ended queue), as long as you use only standard operations of a queue.
You may assume that all operations are valid (for example, no pop or top operations will be called on an empty stack).

就是对java中queue的复习，附上代码：

class MyStack {

    private Queue<Integer> myqueue;  

    MyStack(){
        myqueue = new LinkedList<Integer>();
    }

    // Push element x onto stack.
    public void push(int x) {
        Queue tmp = new LinkedList<Integer>();
        tmp.add(x);
        while(myqueue.size() != 0){
            int data = myqueue.poll();
            tmp.add(data);
        }
        myqueue = tmp;
    }

    // Removes the element on top of the stack.
    public void pop() {
        myqueue.poll();
    }

    // Get the top element.
    public int top() {
        return myqueue.peek();
    }

    // Return whether the stack is empty.
    public boolean empty() {
        return myqueue.size() == 0;
    }
}

题目链接：`https://leetcode.com/problems/implement-stack-using-queues/