206 反转链表

1. 反转链表 给你单链表的头节点 head ，请你反转链表，并返回反转后的链表。

java /** * 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; while(head != null){ ListNode temp = head.next; head.next = pre; pre = head; head = temp; } return pre; } }