LeetCode: Reverse Linked List

 1 /**
 2  * Definition for singly-linked list.
 3  * public class ListNode {
 4  *     public int val;
 5  *     public ListNode next;
 6  *     public ListNode(int x) { val = x; }
 7  * }
 8  */
 9 public class Solution {
10     public ListNode ReverseList(ListNode head) {
11         if (head == null) return null;
12         ListNode p = head, pPre = null;
13         while (p != null) {
14             ListNode pNext = p.next;
15             p.next = pPre;
16             pPre = p;
17             p = pNext;
18         }
19         return pPre;
20     }
21 }