1
var reverseKGroup = function (head, k) {
2
  let count = 0;
3
  let node = head;
4
  while (node && count != k) {
5
    node = node.next;
6
    count++;
7
  }
8
  if (count == k) {
9
    node = reverseKGroup(node, k);
10
    while (count > 0) {
11
      let temp = head.next;
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      head.next = node;
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      node = head;
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      head = temp;
15
      count--;
16
    }
17
    head = node;
18
  }
19
  return head;
20
};