方法一 迭代

 1 /**
 2  * Definition for singly-linked list.
 3  * function ListNode(val) {
 4  *     this.val = val;
 5  *     this.next = null;
 6  * }
 7  */
 8 /**
 9  * @param {ListNode} head
10  * @return {ListNode}
11  */
12 var reverseList = function(head) {
13     let prev = null;
14     let curr = head;
15     while(curr) {
16         const next = curr.next;
17         curr.next = prev;
18         prev = curr;
19         curr = next;
20     }
21     return prev;
22 };

 

方法二 递归

 1 /**
 2  * Definition for singly-linked list.
 3  * function ListNode(val) {
 4  *     this.val = val;
 5  *     this.next = null;
 6  * }
 7  */
 8 /**
 9  * @param {ListNode} head
10  * @return {ListNode}
11  */
12 var reverseList = function(head) {
13     if(head == null || head.next == null) return head;
14     const newHead =  reverseList(head.next);
15     head.next.next = head;
16     head.next = null;
17     return newHead;
18 };