leetcode反转链表

public class ListNode{
    int val;
 ListNode next;
   ListNode(int x) {val = x; }
}

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

}