Leetcode 1721. Swapping Nodes in a Linked List

 /**

 * Definition for singly-linked list.

 * public class ListNode {

 *     int val;

 *     ListNode next;

 *     ListNode() {}

 *     ListNode(int val) { this.val = val; }

 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }

 * }

 */

class Solution {

    public ListNode swapNodes(ListNode head, int k) {    

        // Step 1: Find length of the list

        ListNode curr = head;

        int n = 0;

        while(curr != null) {

            n++;

            curr = curr.next;

        }

        // Step 2: Find kth node from the start and kth node from the end

        ListNode first = head;

   

        for(int i=1; i<k; i++) {

            first = first.next;

        }

        ListNode second = head;

        for(int j=1; j<n-k+1; j++) {

            second = second.next;

        }

        int temp = first.val;

        first.val = second.val;

        second.val = temp;

       

        return head;

    }

}