How should I practice Linked List Cycle Entry Node?

Start by reading the full statement, solve the visible examples, then compare the pattern against related Google onsite interview problems in FastPrep.

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Problem · Linked List

Linked List Cycle Entry Node

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Problem statement

A singly linked list is serialized by an integer array next. Node i points to node next[i]; a value of -1 means that node has no successor. Node 0 is the head, and every represented node is reachable by repeatedly following successors from the head before traversal stops or repeats a node.

If the list contains a cycle, return the zero-based index of the first node in that cycle. Otherwise, return -1.

Function

findCycleEntry(next: int[]) → int

Examples

Example 1

next = [1,2,3,1]return = 1

The traversal is 0 -> 1 -> 2 -> 3 -> 1. Node 1 is the first node in the cycle.

Example 2

next = [1,2,3,-1]return = -1

The traversal reaches node 3 and then stops, so the list has no cycle.

Example 3

next = [0]return = 0

The head points to itself, so node 0 is the cycle entry.

Constraints

1 <= next.length <= 2 * 10^5.
Every next[i] is either -1 or an integer from 0 through next.length - 1.
Every represented node is reachable from node 0 before traversal stops or first repeats a node.