92.反转链表 II

[zzcyes]

Title	Describe
题目	92.反转链表 II
难度	⭐⭐

题目

反转从位置 m 到 n 的链表。请使用一趟扫描完成反转。

说明:
1 ≤ m ≤ n ≤ 链表长度。

示例:

输入: 1->2->3->4->5->NULL, m = 2, n = 4
输出: 1->4->3->2->5->NULL

[zzcyes]

题解

方法一

/**
 * Definition for singly-linked list.
 * function ListNode(val) {
 *     this.val = val;
 *     this.next = null;
 * }
 */
/**
 * @param {ListNode} head
 * @param {number} m
 * @param {number} n
 * @return {ListNode}
 */
var reverseBetween = function(head, m, n) {
  let count = n - m;
  let p = (dummyHead = new ListNode());
  let pre, cur, front, tail;
  p.next = head;
  for (let i = 0; i < m - 1; i++) {
    p = p.next;
  }
  front = p;
  pre = tail = p.next;
  cur = pre.next;
  for (let i = 0; i < count; i++) {
    let next = cur.next;
    cur.next = pre;
    pre = cur;
    cur = next;
  }
  front.next = pre;
  tail.next = cur;
  return dummyHead.next;
};