Coding (Algo)

Linked list cycle detection: use fast and slow pointers to detect repeated traversal state

Linked list cycle detection: A linked structure is represented by a next array where each entry is another index or null. Starting at head, return whether traversal enters a cycle.

Input: A JSON object { "next": (number|null)[], "head": number|null }.

Output: A JSON boolean.

Constraints:

0 <= next.length <= 100000
Every non-null next index is within bounds
head is null or a valid index

Read one JSON value from stdin and print exactly one JSON-serialized answer to stdout with no extra text.

Difficulty: HARD. Variant: 18. Favor a pragmatic solution that is easy to ship, read, and adapt.

Practice context

This coding (algo) exercise trains prompt interpretation, explicit assumptions, a concrete response, and a concise explanation of the decisions made. It is marked hard difficulty.

The signed-in workspace provides the tools required by the round, such as recording, code exec

What this task practices

This coding (algo) exercise trains the same sequence expected in an interview: understand the prompt, make assumptions explicit, produce a concrete answer, and explain the decisions behind it. The task is marked hard difficulty. The private workspace adds the tools required by this round, such as recording, code execution, diagrams, evidence panels, or structured notes. It also preserves the attempt so later feedback can be compared with previous work. Evaluation is based on task-specific criteria and the candidate seniority selected in the preparation path. Public pages never expose the reference solution, hidden tests, evaluator instructions, or another candidate’s work.