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.  * @param {number} left
    11.  * @param {number} right
    12.  * @return {ListNode}
    13.  */
    14. var reverseBetween = function (head, left, right) {
    15.     const node = new ListNode(null)
    17.     node.next = head
    19.     let pre = node
    21.     for (let i = 0; i < left - 1; ++i) {
    22.         pre = pre.next
    23.     }
    25.     let cur = pre.next
    27.     for (let i = 0; i < right - left; ++i) {
    28.         const next = cur.next
    30.         cur.next = next.next
    31.         next.next = pre.next
    32.         pre.next = next
    33.     }
    34.     return node.next
    35. };