Implement Stack using Queues

来源：互联网发布：21天学通c语言第7版编辑：程序博客网时间：2024/05/29 03:20

1 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 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).

题目出处：https://leetcode.com/problems/implement-stack-using-queues/

2 解题思路

1.题目的意思是使用队列实现栈的操作，这两个数据结构的主要区别在于一个将元素加入到尾部，一个将元素加入头部，因此考虑使用两个队列来处理这两种差异方式，始终保持一个队列为空，每次添加元素时，添加到空队列中，然后将非空队列添加到该队列中，并清空。

2.注意一下java中Queue的用法，参考网址：http://www.cnblogs.com/linjiqin/archive/2013/05/30/3107656.html

3 源代码

package com.larry.easy;import java.util.Arrays;import java.util.LinkedList;import java.util.Queue;/** * 使用两个Queue来实现栈 * @author admin * */public class ImplementStackUsingQueues {//始终保持一个队列为空；添加时，添加到空队列，然后将另一个加入private Queue<Integer> que1 = new LinkedList<Integer>();//使用Queue时采用这种方式private Queue<Integer> que2 = new LinkedList<Integer>();// Push element x onto stack.    public void push(int x) {        if(que1.isEmpty()) {        que1.offer(x);        que1.addAll(que2);        que2.clear();        }else{        que2.offer(x);        que2.addAll(que1);        que1.clear();        }    }    // Removes the element on top of the stack.    public void pop() {        if(!que1.isEmpty()) que1.poll();        if(!que2.isEmpty()) que2.poll();    }    // Get the top element.    public int top() {    if(!que1.isEmpty()) return que1.peek();    if(!que2.isEmpty()) return que2.peek();        return 0;    }    // Return whether the stack is empty.    public boolean empty() {    if(que1.isEmpty() && que2.isEmpty()) return true;    else return false;    }        public static void main(String[] args) {ImplementStackUsingQueues isuq = new ImplementStackUsingQueues();isuq.push(1);isuq.push(2);isuq.pop();System.out.println(isuq.top());}}

0 0