反转链表

public class Solution {
    public ListNode ReverseList(ListNode head) {
        if(head == null || head.next == null)//考虑特殊情况
           return head;
        
        ListNode pre = null; //三个指针推动
        ListNode next = null;
       

        while(head!=null)

{next=head.next;

head.next = pre;

pre = head;

head=next;

}

return pre;

 }