[Leetcode]225. Implement Stack using Queues

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).

比较基本的stack的操作，直接上代码

class MyStack {
    Queue<Integer> q = new LinkedList<Integer>();
    // Push element x onto stack.
    public void push(int x) {
        q.add();
    }

    // Removes the element on top of the stack.
    public void pop() {
        int size = q.size();
        for(int i = 1; i < size; i++)
            q.add(q.remove());
        q.remove();
    }

    // Get the top element.
    public int top() {
        int size = q.size();
        for(int i = 1; i < size; i++)
            q.add(q.remove());
        int ret = q.remove();
        q.add(ret);
        return ret;
    }

    // Return whether the stack is empty.
    public boolean empty() {
        return q.isEmpty();     
    }
}