1721. Swapping Nodes in a Linked List

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 <= 10^5

• 0 <= Node.val <= 100

Solution (Java)

/**
 * 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) {
        ListNode beg = null;
        ListNode end = null;
        ListNode node = head;
        while (node != null) {
            k--;
            if (k == 0) {
                beg = node;
                end = head;
            } else if (end != null) {
                end = end.next;
            }
            node = node.next;
        }
        if (beg != null) {
            int tem = beg.val;
            beg.val = end.val;
            end.val = tem;
        }
        return head;
    }
}

Explain:

nope.

Complexity:

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