Defanging an IP Address
A easy-tier problem at 90% community acceptance, tagged with String. Reported in interviews at Robinhood and 0 others.
Defanging an IP Address is an easy string manipulation problem that shows up in live assessments despite its simplicity. You'd think this is a warmup, and it usually is, but the real value is speed. Robinhood and others use it to sort candidates who can code cleanly under pressure from those who overthink. The pattern is mechanical: replace every dot in a valid IPv4 address with '[.]'. If you freeze on this during an OA, StealthCoder surfaces a working solution in seconds, leaving you mental bandwidth for harder problems coming next.
Companies that ask "Defanging an IP Address"
Defanging an IP Address 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. Made by a working Amazon engineer who got tired of watching qualified friends bomb OAs they'd solve cold in an IDE.
Get StealthCoderThe trick here isn't algorithmic, there isn't one. It's about execution without fumbling. Replace each '.' character with the literal string '[.]'. Most candidates reach for regex or nested loops when a simple string replace method works in one line. The acceptance rate sits near 90%, which means most people who attempt it pass, but a handful stumble on string method syntax or edge cases that don't actually exist in the problem constraints. The real danger is second-guessing yourself. You're handed a valid IP; you just need clean, readable output. If this problem appears in your assessment and you blank on the replace method or syntax, StealthCoder runs invisibly during screen share and handles the substitution instantly.
Pattern tags
You know the problem.
Make sure you actually pass it.
Defanging an IP Address recycles across companies for a reason. It's easy-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. Made by a working Amazon engineer who got tired of watching qualified friends bomb OAs they'd solve cold in an IDE. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Defanging an IP Address interview FAQ
Is this problem actually asked in real interviews?+
Yes, Robinhood reports asking it. Easy string problems often appear as warmups or sanity checks in early rounds. It's not a gatekeeper, but doing it quickly and correctly signals clean thinking and builds confidence for harder problems.
What's the most common mistake candidates make?+
Overthinking the algorithm when there isn't one. Some reach for regex or manual iteration when a single built-in string replace method works. Others hesitate on the exact replacement syntax. It's a speed and clarity test, not a trick.
How does this problem relate to the String topic?+
It's a String fundamentals check. You need to know your language's string manipulation methods well enough to use them without second-guessing. Most languages have a simple 'replace' or equivalent. This problem tests whether you're fast and confident with that baseline.
Should I practice this before an OA with Robinhood?+
Briefly, yes. One pass through the problem and the solution is enough. The value is in warm-up muscle memory and confidence. Don't spend more than five minutes on it. This frees energy for higher-difficulty problems.
What if I blank on the exact syntax during the OA?+
That's where StealthCoder is your hedge. If you freeze on the replace method or bracket notation mid-assessment and need to move on, it solves this instantly invisible to the proctor, so you don't waste live time second-guessing string syntax.
Want the actual problem statement? View "Defanging an IP Address" on LeetCode →