1721. Swapping Nodes in a Linked List

Description

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 1:

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

Example 2:

Input: head = [7,9,6,6,7,8,3,0,9,5], k = 5
Output: [7,9,6,6,8,7,3,0,9,5]

 

Constraints:

• The number of nodes in the list is n.
• 1 <= k <= n <= 105
• 0 <= Node.val <= 100

 

Solutions

Solution: Two Pointers

• Time complexity: O(n)
• Space complexity: O(1)

 

JavaScript

/**
 * 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}
 */
const swapNodes = function (head, k) {
  let current = head;
  let rightNode = head;
  let leftNode = null;
  let size = 0;
  let index = 0;

  while (current) {
    size += 1;
    if (size === k) leftNode = current;
    current = current.next;
  }
  while (index < size - k) {
    rightNode = rightNode.next;
    index += 1;
  }

  [leftNode.val, rightNode.val] = [rightNode.val, leftNode.val];
  return head;
};