[LeetCode-JAVA] Implement Stack using Queues

题目:

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 backpeek/pop from frontsize, 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).

题意:用queue来模拟stack,用queue的基本操作

思路:比较简单,用两个queue来进行即可,一个作为模拟的stack存储,一个运来转换中间的操作数字

代码:

class MyStack {
    LinkedList<Integer> queue = new LinkedList<Integer>();
    LinkedList<Integer> temp = new LinkedList<Integer>();
    // Push element x onto stack.
    public void push(int x) {
        while(!queue.isEmpty()){
            temp.offer(queue.poll());
        }
        queue.offer(x);
        while(!temp.isEmpty()){
            queue.offer(temp.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();
    }
}

 

posted @ 2015-06-20 11:40  可爱的波儿胖  阅读(315)  评论(0编辑  收藏  举报

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