reverseInGroups<T> function

LinkedListNode<T>? reverseInGroups<T>(LinkedListNode<T>? head, int k)

Reverses a linked list in groups of specified size

head - The head of the linked list k - The size of each group to reverse Returns the new head of the linked list

Time Complexity: O(n) where n is the length of the list Space Complexity: O(1)

Implementation

LinkedListNode<T>? reverseInGroups<T>(LinkedListNode<T>? head, int k) {
  if (head == null || k <= 1) return head;

  LinkedListNode<T>? current = head;
  LinkedListNode<T>? prev;
  LinkedListNode<T>? next;
  int count = 0;

  // Reverse first k nodes
  while (current != null && count < k) {
    next = current.next;
    current.next = prev;
    prev = current;
    current = next;
    count++;
  }

  // Recursively reverse the remaining nodes
  if (next != null) {
    head.next = reverseInGroups(next, k);
  }

  return prev;
}