141. Linked List Cycle

public boolean hasCycle(ListNode head) {
  ListNode slowPointer = head;
  ListNode fastPointer = head;

  while (fastPointer != null && fastPointer.next != null) {
    slowPointer = slowPointer.next;
    fastPointer = fastPointer.next.next;

    if (slowPointer == fastPointer) {
      return true;
    }
  }

  return false;
}