getCycleLength<T> function

int getCycleLength<T>(LinkedListNode<T>? head)

Calculates the length of the cycle if it exists

head - The head of the linked list Returns the length of the cycle, or 0 if no cycle exists

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

Implementation

int getCycleLength<T>(LinkedListNode<T>? head) {
  if (head == null || head.next == null) return 0;

  LinkedListNode<T>? slow = head;
  LinkedListNode<T>? fast = head;

  // First phase: find the meeting point
  bool hasCycle = false;
  while (fast != null && fast.next != null) {
    slow = slow!.next;
    fast = fast.next!.next;

    if (slow == fast) {
      hasCycle = true;
      break;
    }
  }

  // If no cycle, return 0
  if (!hasCycle) return 0;

  // Second phase: count the length of the cycle
  int length = 1;
  fast = fast!.next;
  while (slow != fast) {
    fast = fast!.next;
    length++;
  }

  return length;
}