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  • Java [Leetcode 225]Implement Stack using Queues

    题目描述:

    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).

    解题思路:

    代码如下:

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

      

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  • 原文地址:https://www.cnblogs.com/zihaowang/p/5164799.html
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