面试16: 反转链表

一. 题目

定义一个函数,输入一个链表的头结点,反转该链表并输出反转后链表的头结点.

代码请到我的代码库中下载 Point2Offer

二. 代码

package com;/** * 剑指offer: 链表反转 * 两种方法求解:1.遍历;2.递归. * 测试用例三种(链表有多个节点,一个节点和链表为空) * @author dingding * Date:2017-6-14 9:55 * Declaration: All Rights Reserved! */public class ReverseList {    public static void main(String[] args) {        test1();        test2();        test3();    }    private static class ListNode{        int value;        ListNode next;    }    //遍历的方式进行反转,返回反转后的头结点(pReversedHead)    private static ListNode reverseListIteratively(ListNode pHead){        ListNode pReversedHead = null;        ListNode pNode = pHead;        ListNode pPrev = null;        while(pNode!=null){            ListNode pNext = pNode.next;            if (pNext==null) {                pReversedHead = pNode;            }            pNode.next = pPrev;            pPrev = pNode;            pNode = pNext;        }        return pReversedHead;    }    //递归方法进行反转,返回下一个递归的节点    private static ListNode reverseListRecursively(ListNode pHead){        if (pHead==null) {            //System.out.println("链表为空!");            return null;        }else {            while (pHead!=null && pHead.next==null){                return pHead;            }            ListNode pNode = reverseListRecursively(pHead.next);            pHead.next.next=pHead;            pHead.next=null;            return pNode;        }    }    private static void printList(ListNode pHead){        if (pHead==null) {            System.out.println("链表为空!");        }else {            while(pHead!=null){                System.out.print(pHead.value+" ");                pHead = pHead.next;            }        }        System.out.println();    }    /*================测试代码================================ */    private static void test(ListNode first){        System.out.println("初始列表:");        printList(first);        System.out.println("遍历方法反转结果:");        ListNode pTail = reverseListIteratively(first);        printList(pTail);        System.out.println("递归方法反转结果:");        ListNode pNode = reverseListRecursively(pTail);        printList(pNode);    }    //输入的链表有多个节点    private static void test1(){        ListNode first = new ListNode();        ListNode second = new ListNode();        ListNode third = new ListNode();        ListNode fourth = new ListNode();        ListNode fifth = new ListNode();        first.value = 1;        second.value = 2;        third.value = 3;        fourth.value = 4;        fifth.value = 5;        first.next = second;        second.next = third;        third.next = fourth;        fourth.next = fifth;        test(first);    }    //输入的链表只有一个结点    private static void test2(){        ListNode first = new ListNode();        first.value=1;        test(first);    }    //输入空链表    private static void test3(){        test(null);    }}

链表类

package com;/** * 链表类 * @author dingding * */public class ListNode {    public int value;    public ListNode next;    public ListNode(int value) {        this.value = value;    }    public int getValue() {        return value;    }    public void setValue(int value) {        this.value = value;    }    public ListNode getNext() {        return next;    }    public void setNext(ListNode next) {        this.next = next;    }}

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有不妥当之处,麻烦告知:D