How should I practice Detect a Linked-List Cycle?

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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Detect a Linked-List Cycle

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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 null. When the array is non-empty, node 0 is the head. Entries that are not reachable from node 0 are ignored.

Return true if following next pointers from the head eventually revisits a node. Return false for an empty list or when traversal reaches null.

Function

hasLinkedListCycle(next: int[]) → boolean

Examples

Example 1

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

Traversal from node 0 enters the cycle 1 -> 2 -> 3 -> 1.

Example 2

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

Traversal reaches node 3 and then null.

Example 3

next = [0]return = true

The head points to itself.

Example 4

next = []return = false

The empty array represents an empty list.

Constraints

0 <= next.length <= 200000.
For every index i, next[i] == -1 or 0 <= next[i] < next.length.