LeetCode 1721: Swapping Nodes in a Linked List Solution

class Solution {
    public ListNode swapNodes(ListNode head, int k) {
        ListNode dummy = new ListNode(0);
        dummy.next = head;
        ListNode fast = dummy, slow = dummy, first = dummy, second = dummy;
        
        // Move fast k nodes ahead
        for (int i = 0; i < k; i++) {
            fast = fast.next;
        }
        
        first = fast;
        
        // Move fast to the end and slow will reach kth node from the end
        while (fast != null) {
            fast = fast.next;
            slow = slow.next;
        }
        
        second = slow;
        
        // Swap values
        int temp = first.val;
        first.val = second.val;
        second.val = temp;
        
        return head;
    }
}