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The CIDR bitmask part I actually got through okay.
Start by clarifying the requirements: rule order matters, so the first matching rule determines the action. Then outline an approach that parses CIDR blocks into integer ranges, checks the IP against each rule in order, and returns the action of the first match, with a default action if no rule matches.
Pro tip: Mention that you would preprocess the rules into a data structure (e.g., sorted intervals or a trie) for efficiency if the function is called repeatedly, but keep the initial implementation simple and correct. This shows awareness of trade-offs between simplicity and performance.
Ask about default action when no rule matches, whether rules are guaranteed to be valid CIDR blocks, and if IPv4 or IPv6 support is needed. Confirm that rule order is significant and the first match wins.
Explain that you will convert each CIDR block into a range of IP addresses (start and end integers) and check if the given IP falls within that range. Iterate through rules in order and return the action of the first matching rule.
Describe how to parse an IP address into a 32-bit integer (for IPv4) and how to compute the network range from a CIDR block using bitwise operations (mask and prefix length).
Write pseudocode or actual code: for each rule, compute the network range, check if the IP is within that range, and if so return the rule's action. If no rule matches, return the default action.
Mention that the simple O(n) per query approach is fine for small rule sets, but for large or frequently queried sets, you could preprocess rules into a trie or sorted intervals for faster lookup, at the cost of increased complexity.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.
Model the ACL as a set of allowed IP ranges (or a binary trie/interval tree) and check whether the query CIDR is fully contained in the union of allowed ranges. Efficiently, convert the CIDR to an integer interval and verify that every sub-interval is covered by allowed ranges, handling overlaps and merging adjacent ranges.
Pro tip: Mention that you can preprocess the ACL into a sorted list of merged intervals or a binary trie for O(log n) queries, and that you must consider edge cases like overlapping rules, default deny, and IPv4 vs IPv6.
Confirm whether the ACL is a list of allow/deny rules with priorities, and whether the query CIDR is IPv4 or IPv6. Establish that 'every IP allowed' means the CIDR must be a subset of the union of allowed ranges.
Convert each IP to a 32-bit (or 128-bit) integer, and each CIDR to a contiguous interval [start, end]. This reduces the problem to interval containment.
Sort allowed intervals by start, merge overlapping or adjacent intervals, and optionally build a balanced interval tree or binary trie for fast queries. This handles rule overlaps and simplifies containment checks.
For the query interval [q_start, q_end], find the allowed interval that contains q_start (via binary search or tree lookup) and verify that its end >= q_end. If not, return DENY.
Discuss time/space trade-offs: preprocessing O(n log n) and query O(log n) with merged intervals, or O(32) with a binary trie. Mention memory vs speed and handling of dynamic ACL updates.
AI-generated suggestions, not part of the candidate's original notes. May be inaccurate — verify before relying on them.