206. 反转链表

解题过程

/*** Definition for singly-linked list.* public class ListNode {*     int val;*     ListNode next;*     ListNode() {}*     ListNode(int val) { this.val = val; }*     ListNode(int val, ListNode next) { this.val = val; this.next = next; }* }*/
class Solution {public ListNode reverseList(ListNode head) {ListNode pre = null;ListNode cur = null;while(head != null){cur = head.next;head.next = pre;pre = head;head = cur;}head = pre;return pre;}
}