Leetcode题解 206. Reverse Linked List

Reverse a singly linked list.

用三个节点保存前、中、后三个节点即可。

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
public class Solution {
    public ListNode reverseList(ListNode head) {
        if(head==null){
            return null;
        }else if(head.next==null){
            return head;
        }
        ListNode prev,last;
        prev=head;
        head=head.next;
        prev.next=null;
        if(head.next==null){
            head.next=prev;
        }else{
           last=head.next;
           while(last!=null){
             head.next=prev;
             prev=head;
             head=last;
             last=last.next;
            }
           head.next=prev; 
        }
        return head;
    }
}