92.反转链表-ii.js

/*
 * @lc app=leetcode.cn id=92 lang=javascript
 *
 * [92] 反转链表 II
 */

// @lc code=start
/**
 * Definition for singly-linked list.
 * function ListNode(val, next) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.next = (next===undefined ? null : next)
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} left
 * @param {number} right
 * @return {ListNode}
 */
// [1, 2, 3, | [4, 5, 6], 7, 8, 9]
var reverseBetween = function(head, left, right) {
  if (left == 1) {
    return reverseN(head, right) // reverse first N value!
  }
  head.next = reverseBetween(head.next, left - 1, right - 1)
  return head
}

let successor = null
function reverseN(head, n) {
  if (n == 1) {
    successor = head.next
    return head
  }
  const last = reverseN(head.next, n - 1)
  head.next.next = head
  head.next = successor
  return last
}

// @lc code=end

module.exports = { reverseBetween }