Design an IPv4 Address Iterator
Company: Anthropic
Role: Software Engineer
Category: Coding & Algorithms
Difficulty: medium
Interview Round: Technical Screen
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?
Quick Answer: 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 the logic for an IPv4 address iterator.
An IPv4 address is a string in the form `a.b.c.d`, where each octet is an integer from `0` to `255`.
A conceptual iterator is created with:
- `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 iterator behaves like this:
- `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`
- The iterator includes `end_ip` only if it is landed on exactly
For this coding problem, instead of implementing a class, write a function that returns the full list of IPv4 addresses that would be produced by repeated calls to `next()` while `has_next()` is true.
You must 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`
Follow-up to consider: what internal representation makes the implementation simpler and avoids repeated string parsing?
Constraints
- All input IP strings are valid IPv4 addresses with octets in the range 0 to 255.
- `start_ip` is less than or equal to `end_ip` in numeric IPv4 order.