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I parsed the CIDR blocks into integer intervals first, which worked for basic membership checks but felt clunky when they asked about efficiency at scale.
Clarify the problem constraints and edge cases, then propose a solution using a binary trie (prefix tree) to store CIDR rules for efficient longest-prefix match. Discuss trade-offs between trie and sorted list approaches, and handle IPv4/IPv6 considerations.
Pro tip: Mention that you would normalize IP addresses and CIDR blocks to binary form and consider using a compressed trie (Patricia trie) for memory efficiency, especially if rules are numerous.
Ask about IP version (IPv4/IPv6), rule format, expected scale, and whether rules can overlap. Confirm default behavior when no match.
Propose a binary trie where each node represents a bit of the IP address, storing the rule action at the node corresponding to the prefix length. Alternatively, discuss sorted list with binary search.
For each CIDR rule, convert IP and prefix length to binary, traverse/create nodes, and mark the terminal node with the action (approve/reject).
Traverse the trie bit by bit following the query IP's bits, keeping track of the last seen rule action. After traversal, return the last action or default to reject.
Discuss time complexity O(W) per query where W is bit width (32 or 128), and space O(N*W). Compare with sorted list approach O(log N) but with more complex matching.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.