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This question is commonly asked for Software Engineer candidates at Anthropic during technical interviews.

Design an IPv4 Address Iterator | Anthropic Interview Question

Q: Design an IPv4 Address Iterator

This question evaluates a candidate's ability to represent and iterate IPv4 addresses, covering parsing, numeric arithmetic with carry between octets, and the design of a stateful iterator.

Design a class that iterates through IPv4 addresses.

An IPv4 address is a string in the form a.b.c.d, where each octet is an integer from 0 to 255.

Implement an iterator with the following behavior:

The constructor receives:
- start_ip : the first IPv4 address in the sequence
- end_ip : the last IPv4 address that may be returned
- step : a positive integer increment
The increment is fixed for the lifetime of the object and is provided in the constructor, not passed into next() .
next() returns the current IP address and then advances by step addresses.
has_next() returns whether another valid address can still be returned without passing end_ip .

You should correctly handle carry between octets. For example:

incrementing 10.0.0.255 by 1 gives 10.0.1.0
incrementing 192.168.1.254 by 2 gives 192.168.2.0

Assume all input IP strings are valid and start_ip <= end_ip.

Example:

start_ip = "192.168.0.254"
end_ip = "192.168.1.4"
step = 2

The iterator should return:

192.168.0.254
192.168.1.0
192.168.1.2
192.168.1.4

Follow-up: What internal representation would you choose to simplify the implementation and avoid repeated string parsing?