IPv4 Iterators and CIDR
Also known as: IP to CIDR
Part 1: IPv4 Forward Iterator - IPv4Iterator(start_ip) starts at start_ip (inclusive) - next() returns the next IP as dotted string - When exhausted, next() returns "null"
Build practical IPv4 primitives: forward/reverse iterators, CIDR range expansion, and (finally) covering N sequential IPs with minimum CIDR blocks. This tests bitwise thinking, boundary discipline, and writing clear stateful code.
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