ReverseNodesInKGroups.swift

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 */

// Given a linked list, reverse the nodes of a linked list k at a time and return its modified list.

// If the number of nodes is not a multiple of k then left-out nodes in the end should remain as it is.

// You may not alter the values in the nodes, only nodes itself may be changed.
// Only constant memory is allowed.

// Example
// Example 1

// Input:
// list = 1->2->3->4->5->null
// k = 2
// Output:
// 2->1->4->3->5
// Example 2

// Input:
// list = 1->2->3->4->5->null
// k = 3
// Output:
// 3->2->1->4->5


/**
 * Definition for ListNode
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) {
 *         val = x;
 *         next = null;
 *     }
 * }
 */

public class Solution {
  /**
   * @param head: a ListNode
   * @param k: An integer
   * @return: a ListNode
   */
}