Problem

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

Solution

/**
 * 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) {
    if (!head) {
        return null;
    }
    let left = head, right = head;
    for (let i = 1; i < k; i++) {
        left = left.next;
    }
    let curr = left;
    while (curr.next) {
        curr = curr.next;
        right = right.next;
    }
    let temp = left.val;
    left.val = right.val;
    right.val = temp;
    return head;
};

Explain:

nope.

Complexity:

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