# Swapping Nodes in a Linked List

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]

Example 3:

Input: head = [1], k = 1
Output: [1]

Example 4:

Input: head = [1,2], k = 1
Output: [2,1]

Example 5:

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

Constraints:

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

Solution:

/**
* 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 dummy = new ListNode(0);
ListNode prev1 = dummy;
ListNode p2 = null;
int i = 1;
while (p1 != null) {
if (i == k - 1) {
prev1 = p1;
}
if (i == k + 1) {
}
p1 = p1.next;
if (p1 != null && p2 != null) {
p2 = p2.next;
}
i ++;
}
if (p2 == null) {
p2 = dummy;
}
ListNode node1 = prev1.next;
ListNode node2 = p2.next;
int temp = node1.val;
node1.val = node2.val;
node2.val = temp;