反转链表

Posted 2021-02-09 turningli

package com.lkr.dataStructure.linkedlist;

import java.util.LinkedList;

//反转单链表
public class ReverseList {

    public static void main(String[] args){
        ListNode linkNode1 = new ListNode(1);
        ListNode linkNode2 = new ListNode(2);
        ListNode linkNode3 = new ListNode(3);
        ListNode linkNode4 = new ListNode(4);
        ListNode linkNode5 = new ListNode(5);
        ListNode linkNode6 = new ListNode(6);
        linkNode1.next = linkNode2;
        linkNode2.next = linkNode3;
        linkNode3.next = linkNode4;
        linkNode4.next = linkNode5;
        linkNode5.next = linkNode6;
        System.out.println("链表为： ");
        printList(linkNode1);
        System.out.println("
链表反转后为： ");
        //遍历法
        //reverseList(linkNode1);
        //递归法
        reverseList3(linkNode1);
        //反向输出链表
        // reservePrt(linkNode1);
        printList(linkNode6);

    }

    //打印链表数据
    public static void printList(ListNode node){
        System.out.print(node.data);
        if(node.next != null){
            printList(node.next);
        }

    }

    //遍历法
    public static ListNode reverseList(ListNode head){
        ListNode pReversedHead =null;    //反转后的单链表头节点
        ListNode pNode = head;      //定义pNode指向head
        ListNode pPre = null;      //定义存储前一个节点
        while (pNode != null){
            ListNode pNext = pNode.next;    //定义pNext指向pNode下一个节点
            if(pNext != null){      //如果pNode下一个节点为空，则pNode即为结束
                pReversedHead = pNode;
            }
            pNode.next = pPre;  //修改pNode指针域指向pPre
            pPre = pNode;       //复制pNode到pPre
            pNode = pNext;      //将pNode的下一个节点复制给pNext
        }
        return pReversedHead;
    }

    //递归实现

    public static ListNode reverseList3(ListNode pHead){
        if(pHead==null || pHead.next == null){ //如果没有结点或者只有一个结点直接返回pHead
            return pHead;
        }
        ListNode pNext = pHead.next; //保存当前结点的下一结点
        pHead.next = null; //打断当前结点的指针域
        ListNode reverseHead = reverseList3(pNext); //递归结束时reverseHead一定是新链表的头结点
        pNext.next = pHead; //修改指针域
        return reverseHead;
    }

    //反向输出链表
    public static void reservePrt(ListNode node){
        if(node != null){
            reservePrt(node.next);
            System.out.print(node.data+" ");
        }
    }

}