翻转链表

定义一个结点类：

class Node {
    int val;
    Node next;

    public Node(int val) {
        this.val = val;

    }
}

图解：【这里以头删+头插为例】

 

 

翻转链表：

package com.basic.datastructure;

//翻转链表
public class ReverseListNode {

    //1.头插+头删
    public static Node reverseListNode(Node head){
        if(head==null || head.next==null) return head;
        Node cur=head;
        Node newNode=null;
        while(cur!=null){
            Node node=cur.next;
            cur.next=newNode;
            newNode=cur;
            cur=node;
        }
        return newNode;
    }

    //2.就地反转
    public  static Node reverseList(Node head){
        if(head==null || head.next==null){
            return head;
        }

        Node cur=head;
        Node prev=null;

        while(cur!=null){
            Node node=cur.next;
            cur.next=prev;
            prev=cur;
            cur=node;
        }
        return prev;
    }
    //打印链表结点
    public  static void printListNode(Node head){
        Node cur=head;
        while(cur!=null){
            System.out.print(cur.val+",");
            cur=cur.next;
        }

    }

    public static void main(String[] args) {
        Node node1=new Node(1);
        Node node2=new Node(2);
        Node node3=new Node(3);
        Node node4=new Node(4);
        Node node5=new Node(5);
        node1.next=node2;
        node2.next=node3;
        node3.next=node4;
        node4.next=node5;

        printListNode(node1);
        System.out.println();

        //Node rst=reverseListNode(node1);
        Node rst=reverseList(node1);
        printListNode(rst);

    }
}

运行结果：