Greatest Common Divisor of Strings
A easy-tier problem at 53% community acceptance, tagged with Math, String. Reported in interviews at Datadog and 2 others.
Greatest Common Divisor of Strings hits your OA and looks deceptively simple: find the longest string that divides both inputs evenly. Datadog, Nvidia, and Infosys ask it. The problem catches people because the string logic masks a pure math pattern. The acceptance rate is just over 50%, which means half the candidates either overthink the recursion or miss the GCD trick entirely. If you freeze on the pattern during your assessment, StealthCoder solves it invisible to the proctor in seconds.
Companies that ask "Greatest Common Divisor of Strings"
Greatest Common Divisor of Strings 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 by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share.
Get StealthCoderThe trap is building string combinations to find overlap. The actual move is recognizing that if a GCD string exists, both inputs must be made of that substring repeated. The solution is pure GCD math on the string lengths, then validate the substring. You compute GCD of len(str1) and len(str2) using Euclid's algorithm, extract a candidate substring of that length, then check if both original strings are repetitions of it. Common failure: trying character-by-character comparison or brute force substring matching instead of leaning on number theory. The Math and String topics work together here, not separately. During a live OA, if the math connection doesn't click immediately, StealthCoder is your safety net to surface the GCD approach and working code before panic sets in.
Pattern tags
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Make sure you actually pass it.
Greatest Common Divisor of Strings 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. Built by an engineer at a top-10 tech company who can solve these problems cold but didn't want to trust himself in a 90-minute screen share. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Greatest Common Divisor of Strings interview FAQ
Is this really just a GCD problem in disguise?+
Yes. The trick is that a valid GCD string must divide both inputs as repetitions. Compute GCD of the two string lengths, extract substring at that length from the first string, then verify both strings are that substring repeated. Skip the string-building search entirely.
Why do so many people fail if it's marked Easy?+
The 50% acceptance rate suggests most candidates attack it with string search or brute force instead of recognizing the math pattern. The problem statement doesn't hint at GCD or Euclidean algorithm, so candidates waste time on the wrong approach before time runs out.
Do Datadog and Nvidia expect both Math and String solutions?+
The Math approach is the optimal one. Interviewers at those companies likely ask follow-ups like edge cases (empty strings, single characters) and space optimization, but the core solution leans Math. String iteration won't get you full marks.
What's the edge case that catches people?+
When str1 + str2 does not equal str2 + str1, no GCD string exists. Many candidates skip this check or fail on empty string inputs. Validate concatenation equality first before computing GCD to avoid false positives.
How does this problem relate to the broader Math and String topics?+
It's the intersection. You apply pure Math (Euclidean GCD) but the input is strings and the output is a string. Understanding the dual nature is the actual skill being tested, not just coding one algorithm.
Want the actual problem statement? View "Greatest Common Divisor of Strings" on LeetCode →