← Databricks Interview Insights
Started with a trie on the bit representation of the IP, which felt right since CIDR rules are basically prefix matches.
Start by clarifying requirements and constraints, then propose a trie-based data structure for efficient longest-prefix matching on a single IP. For CIDR range matching, extend the trie to handle range queries or use interval trees, and discuss trade-offs between approaches.
Pro tip: Mention that real-world systems often use a combination of tries and interval trees, and that rule ordering matters for overlapping CIDRs—demonstrating awareness of production complexities.
Ask about rule priority (e.g., longest prefix match, first match), expected scale, and whether rules can overlap. This shows you think about edge cases before coding.
Propose a binary trie (prefix tree) where each node represents a bit of the IP address, storing accept/deny at terminal nodes. Explain that lookup is O(32) for IPv4, and discuss handling of default rules.
For an incoming CIDR range, you need to check if any rule CIDR overlaps or contains it. Discuss approaches: decompose the range into prefixes and query the trie, or use an interval tree for efficient overlap queries.
Compare trie vs. interval tree vs. sorted arrays with binary search. Mention memory vs. speed trade-offs, and how to handle updates (insert/delete rules) efficiently.
Bring up real-world aspects: rule ordering, default policies, performance under high throughput, and potential use of hardware acceleration or caching.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.