You are given the head of a linked list, and an integer k.

Return the head of the linked list after swapping the values of the kth node from the beginning and the kth node from the end (the list is 1-indexed).

Example

Input: (head = [1, 2, 3, 4, 5]), (k = 2);
Output: [1, 4, 3, 2, 5];

Solution

Great solution found here

/**
 * 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} k
 * @return {ListNode}
 */
var swapNodes = function (head, k) {
  //Set fast, second, and first to head
  let fast = head,
    second = head,
    first = head;
  //For k - 1 times
  for (let i = 0; i < k - 1; i++) {
    fast = fast.next;
  }
  first = fast;
  while (fast.next != null) {
    fast = fast.next;
    second = second.next;
  }
  let temp = first.val;
  first.val = second.val;
  second.val = temp;
  return head;
};