题解 | #翻转链表#

import java.util.Scanner;
class LinkedList2 {
    class ListNode {
        public int val;
        public ListNode prev;
        public ListNode next;
        public ListNode(int val) {
            this.val = val;
        }
    }
    public ListNode head;
    public ListNode last;
    public void addBack(int val) {
        ListNode Node = new ListNode(val);
        if (head == null) {
            head = Node;
            last = Node;
            return;
        }
        last.next = Node;
        Node.prev = last;
        last = Node;

    }
    public int size(ListNode head){
        int count=0;
        if(head==null){
            return 0;
        }
        ListNode tail = head;
        while(tail.next!=null){
            count++;
            tail = tail.next;
        }
        return count;
    }
    public ListNode resever(ListNode head,ListNode last){
          ListNode Node = new ListNode(0);
          ListNode tmp = Node;
          ListNode cur = head;
         ListNode tail = last;
         ListNode slow=head;
         int count=0;
         ListNode flast=head;
         while(flast!=null&&flast.next!=null){
             count++;
             flast=flast.next.next;
             slow =slow.next;
         }
         if(size(head)%2==0){
             count++;
         }
         while(count-->0){
             tmp.next=cur;
             cur.prev=tmp;
             cur=cur.next;
             tmp=tmp.next;
             tmp.next=tail;
             tail = tail.prev;
             tail.next.prev=tmp;
             tmp=tmp.next;
         }
         tmp.next =cur;
         tmp.next=null;
         return Node.next;
    }
    public void display(ListNode head){

        if(head==null){
            return;
        }
       ListNode tail =head;
        while(tail!=null){
            System.out.print(tail.val);
            if(tail.next!=null){
                System.out.print(",");
            }
            tail = tail.next;
        }

    }
}

public class Main {
    public static void getcreate( LinkedList2 head ,String str) {
        String[] ret = str.split(",");
        for (int i = 0; i < ret.length; i++) {
            int a = Integer.parseInt(ret[i]);
            head.addBack(a);
        }
    }
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        String str = scanner.nextLine();
        LinkedList2 link = new LinkedList2();
        LinkedList2 link2 = new LinkedList2();
        LinkedList2 link3 = new LinkedList2();
        getcreate(link,str);
     LinkedList2.ListNode tmp= link2.resever(link.head,link.last);
      link3.display(tmp);
    }
}

双向循环链表，注意判断链表长度奇数偶数。奇数偶数在临界的时候要做处理。