[LeetCode]206. Reverse Linked List(链表反转)

Reverse a singly linked list.

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利用循环。

 public class Solution {
     public ListNode reverseList(ListNode head) {
         if(head == null ||head.next == null) return head;
         ListNode pre = head;
         head = head.next;
         pre.next = null;
         while(head != null){
             ListNode next = head.next;
             head.next = pre;
             pre = head;
             head = next;
         }
         return pre;
     }
 }

递归版

 public class Solution {
     public ListNode reverseList(ListNode head) {
         if(head == null ||head.next == null) return head;
         ListNode pre = head;
         head = head.next;
         ListNode newhead = reverseList(head);
         pre.next = null;
         head.next = pre;
         return newhead;

     }
 }