Full Circle

A medium Python interview practice problem on DataDriven. Write and execute real python code with instant feedback.

Domain

Python

Difficulty

medium

Seniority

L3

Problem

A forwarding table is stored as a flat array `next_indices`, where each slot holds the index it forwards to next, or -1 to mark the end of a chain. Starting from slot 0 and following the pointers, return the index of the first slot the walk reaches twice, or -1 if it ends first. A pointer of -1, or one that falls outside the array, ends the walk rather than closing a loop.

Summary

Follow the chain long enough and it might loop back.

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