一、使用循环

  1. /**
  2.  * Definition for singly-linked list.
  3.  * function ListNode(val, next) {
  4.  *     this.val = (val===undefined ? 0 : val)
  5.  *     this.next = (next===undefined ? null : next)
  6.  * }
  7.  */
  8. /**
  9.  * @param {ListNode} head
  10.  * @return {ListNode}
  11.  */
  12. var reverseList = function(head) {
  13.     if(!head || !head.next) {
  14.       return head
  15.     }
  17.     let pre = null
  18.     let cur = head
  19.     let tmp = head.next
  21.     while(cur) {
  22.       cur.next = pre
  23.       pre = cur
  24.       cur = tmp
  25.       tmp = cur && cur.next
  26.     }
  28.     return pre
  29. };

二、使用递归

  1. /**
  2.  * @param {ListNode} head
  3.  * @param {ListNode} p
  4.  * @return {ListNode}
  5.  */
  6. var reverseList = function(head, p = null) {
  7.   if (!head.value) return head
  9.     const next = head.next
  11.     head.next = p
  12.     return next ? reverseList(next, head) : head
  13. };