LeetCode-Implement Stack using Queues-蒲公英云

LeetCode-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).

一个队列即可完成，上代码：

class MyStack {
    LinkedList<Integer> queue = new LinkedList<Integer>();
    // Push element x onto stack.
    public void push(int x) {
        queue.add(x);
        for (int i = 0; i < queue.size()-1; i++) {
            queue.add(queue.poll());
        }
    }
    // Removes the element on top of the stack.
    public void pop() {
        queue.poll();
    }
    // Get the top element.
    public int top() {
        return queue.peek();
    }
    // Return whether the stack is empty.
    public boolean empty() {
        return queue.isEmpty();
    }
}