Your question is Linked List Reverse or Cycle. Start with the requirements on the right.
Run and submit as often as you like. When you're ready, talk me through your approach or go straight to the code.
People's QA checks sometimes model workflow transitions as a linked sequence of states. Given an array representation of those transitions, determine whether the sequence starting at head eventually loops back to a previously visited state.
Each array index represents one state, and next_indices[i] gives the index of the next state. A value of -1 indicates the end of the sequence. Return True if a cycle exists and False otherwise. Solve the problem with O(1) additional space using two pointers moving at different speeds.
Implement detect_cycle(next_indices, head).
next_indices, a list of integers, and head, an integer index. Each pointer is either -1 or a valid index in next_indices.def detect_cycle(next_indices, head):