反转一个单链表。
示例:
输入: 1->2->3->4->5->NULL 输出: 5->4->3->2->1->NULL
/** * Definition for singly-linked list. * public class ListNode { * int val; * ListNode next; * ListNode(int x) { val = x; } * } */ class Solution { public ListNode reverseList(ListNode head) { ListNode root = null;; return Reverse(head, root); } public ListNode Reverse(ListNode head, ListNode returnNode) { if(head == null) return returnNode; ListNode next = head.next; head.next = returnNode; return Reverse(next, head); } }
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