IP to CIDR
A medium-tier problem at 55% community acceptance, tagged with String, Bit Manipulation. Reported in interviews at Databricks and 1 others.
IP to CIDR is a medium-difficulty string and bit manipulation problem that combines low-level network knowledge with algorithmic thinking. Databricks and Airbnb both ask it, and it sits right at the edge of what candidates usually prep for. The problem forces you to convert a list of IP addresses into the smallest set of CIDR blocks that cover them all, which sounds simple until you realize you need to reason about bit patterns and block boundaries simultaneously. If this hits your live OA and you blank on the merging logic, StealthCoder solves it in seconds, invisible to the proctor.
Companies that ask "IP to CIDR"
IP to CIDR is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround.
Get StealthCoderThe trap here is thinking this is just sorting and grouping. The real work is recognizing that valid CIDR blocks must start at power-of-2 boundaries and span power-of-2 ranges. You convert each IP to a 32-bit integer, then greedily merge adjacent blocks when they align. Most candidates get stuck on the merging criteria or mess up the bit-level comparisons. The bit manipulation piece is mandatory, not optional. Even if you've solved general interval-merging problems before, the CIDR-specific constraints (contiguous ranges, aligned boundaries) require careful handling. StealthCoder is the hedge if you haven't drilled this specific pattern and hit it live.
Pattern tags
You know the problem.
Make sure you actually pass it.
IP to CIDR recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built because the OA filter rejects engineers who'd pass the on-site. That's a broken filter. This is the workaround. Works on HackerRank, CodeSignal, CoderPad, and Karat.
IP to CIDR interview FAQ
Is this really asked at Databricks and Airbnb?+
Yes. Databricks and Airbnb both report this problem in their hiring loops. It's not ultra-frequent, but it appears enough that system design and infrastructure-focused candidates should be ready for it.
Do I need to know networking or just coding?+
You need to understand CIDR notation and how IP addresses map to bit ranges, but the problem statement will explain it. The coding part is the constraint: merge blocks at power-of-2 boundaries. Networking knowledge helps, but the algorithm is the bottleneck.
What's the trick most people miss?+
Assuming any two adjacent IPs can merge into a CIDR block. They can't. You must check that the start address is aligned to the block size (a multiple of a power of 2) and that the block spans a power-of-2 range. Bit manipulation is mandatory.
How does this relate to interval merging problems?+
Interval merging is the skeleton, but CIDR adds structure. Standard interval problems don't care about boundaries or alignment. Here, you're merging intervals with strict alignment rules, which makes greedy approaches trickier and requires careful bit-level reasoning.
Can I solve this without converting IPs to integers?+
Technically yes, but you'd be working with strings and doing manual bit checks, which is slower and error-prone. Converting to 32-bit integers and using bitwise operators is the standard approach and what interviewers expect.
Want the actual problem statement? View "IP to CIDR" on LeetCode →