IPv4 Address Iterator and CIDR

PracticalmediumPremium

45:00

Desktop only

Coding Challenges are optimized for Desktop

Come back on a wider screen - the live editor needs room to breathe. You can still read the problem brief above.

Problem

Network tooling - firewalls, DHCP allocators, load balancers - treats IP addresses as 32-bit integers, not dotted strings. Iterating a CIDR block means walking a range; decomposing an arbitrary range into the minimum set of CIDR blocks is the inverse. You will implement the conversions and both directions of CIDR arithmetic.

Level 1 - Conversion and forward iteration

ip_to_int("192.168.1.1") returns 3232235777.
int_to_ip is the inverse.
IPv4Iterator(start, end) yields each IP from start to end inclusive. next() returns None once the range is exhausted.

Validation:

Bad octet count or out-of-range octet -> ValueError.
n outside [0, 0xFFFFFFFF] -> ValueError.

Example:

ip_to_int("192.168.1.1")     -> 3232235777
int_to_ip(3232235777)        -> "192.168.1.1"
 
it = IPv4Iterator("10.0.0.1", "10.0.0.3")
it.next()  -> "10.0.0.1"
it.next()  -> "10.0.0.2"
it.next()  -> "10.0.0.3"
it.next()  -> None   # exhausted

Level 2 - CIDR parsing

def cidr_to_range(cidr: str) -> tuple[str, str]:
    """'192.168.1.0/24' -> ('192.168.1.0', '192.168.1.255'). Returns the network
    and broadcast addresses of the block."""

/0 covers the full IPv4 space.
/32 is a single address (network == broadcast).
The base address need not already be aligned; canonicalize it to the network address.

Example:

cidr_to_range("192.168.1.0/24")
  -> ("192.168.1.0", "192.168.1.255")
 
cidr_to_range("192.168.1.5/24")   # non-aligned base
  -> ("192.168.1.0", "192.168.1.255")
 
cidr_to_range("10.0.0.1/32")
  -> ("10.0.0.1", "10.0.0.1")

Level 3 - Range to minimum CIDR cover

def range_to_cidr_blocks(start: str, end: str) -> list[str]:
    """Decompose [start, end] into the smallest set of aligned CIDR blocks."""

Cover [start, end] exactly with the fewest aligned CIDR blocks. At each step, take the largest block aligned to the current start that doesn't overshoot end, advance past it, and repeat.

Example:

range_to_cidr_blocks("10.0.0.1", "10.0.0.7")
  -> ["10.0.0.1/32", "10.0.0.2/31", "10.0.0.4/30"]
 
range_to_cidr_blocks("0.0.0.0", "255.255.255.255")
  -> ["0.0.0.0/0"]

Patterns used

Foundations primers this challenge draws on.

Bit Manipulation

Loading editor...

The live editor for this challenge unlocks with Premium.

Browse free problems

0/0 passed