reverse_linked_list_recursive.js

// Reverse a singly linked list.
//
//     Example:
//
// Input: 1->2->3->4->5->NULL
// Output: 5->4->3->2->1->NULL
// Follow up:
//
//     A linked list can be reversed either iteratively or recursively. Could you implement both?

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @return {ListNode}
 */

const reverseList = function(head) {
  if (!head || !head.next) {
    return head;
  }
  let tmp = reverseList(head.next); //?
  head.next.next = head;
  head.next = undefined;
  return tmp;
};