力扣挑战赛第13天-No.19删除链表的倒数第N个结点

题目描述

给你一个链表，删除链表的倒数第 n 个结点，并且返回链表的头结点。

示例：

输入：head = [1,2,3,4,5], n = 2
输出：[1,2,3,5]

输入：head = [1], n = 1
输出：[]

输入：head = [1,2], n = 1
输出：[1]

注意：

链表中结点的数目为 sz
1 <= sz <= 30
0 <= Node.val <= 100
1 <= n <= sz

解法

双指针（快慢指针）

/**
 * 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} n
 * @return {ListNode}
 */
let removeNthFromEnd = function (head, n) {
  if (!head.next) {
    return null;
  }
  let dummyNode = new ListNode();
  dummyNode.next = head;
  let slow = dummyNode;
  let fast = head;
  while (n - 1) {
    fast = fast.next;
    n--;
  }
  while (fast.next) {
    slow = slow.next;
    fast = fast.next;
  }
  slow.next = slow.next.next;
  return dummyNode.next;
};

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