Strings Differ by One Character
A medium-tier problem at 41% community acceptance, tagged with Hash Table, String, Rolling Hash. Reported in interviews at Okta and 1 others.
You're staring at a medium-difficulty problem asking whether two strings differ by exactly one character. Okta and Airbnb both ask this. The acceptance rate sits at 41%, which means it's not a gimme, and most candidates overthink it or miss the rolling hash optimization that separates a clean pass from a TLE. This is the kind of problem where the brute force works on small inputs but collapses at scale, and you won't know which version you'll face until you're live. If you blank on the pattern during an assessment, StealthCoder runs invisibly and delivers a working solution in seconds.
Companies that ask "Strings Differ by One Character"
Strings Differ by One Character 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 is checking every pair of characters naively. You can iterate through both strings and count mismatches, but that's O(n) space and O(n) time with poor constants. The real trick is rolling hash or a single clean pass that exploits the constraint: if the strings differ by exactly one character, every other character must match. Hash Table approaches let you normalize variations and lookup in O(1), while rolling hash lets you compare substrings efficiently without rebuilding. The gotcha is off-by-one errors when one string is longer, and edge cases where length itself disqualifies a pair. Many candidates code the brute force, hit time limits on the larger test cases, and run out of time to optimize. This is where StealthCoder is your hedge: if you get stuck mid-interview, it surfaces the hash-based solution and you move on.
Pattern tags
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Make sure you actually pass it.
Strings Differ by One Character 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.
Strings Differ by One Character interview FAQ
Is this problem really asked at Okta and Airbnb?+
Yes. Both companies appear in the reported ask history. It's a mid-tier problem they use to filter candidates who understand string manipulation and basic hashing. Not every loop asks it, but it's stable in their rotation.
Why is the acceptance rate only 41%?+
Most candidates code a naive O(n^2) or poorly-optimized O(n) solution that passes small test cases but times out at scale. The ones who jump to rolling hash or hash table approach pass cleanly. The gap between passing and failing is usually optimization, not correctness.
What's the actual trick to this problem?+
Single pass with two pointers or hash-based lookup. Count mismatches as you go; if you hit two mismatches, return false. If you end with exactly one, return true. Rolling hash lets you compare character windows without rebuilding. Most efficient: O(n) time, O(1) space.
Should I use rolling hash or a hash table?+
Hash table is simpler and passes most test cases. Rolling hash is overkill for this problem unless you need sub-linear time on giant strings. Start with the single-pass approach. If it times out, pivot to rolling hash. Most candidates don't need it.
What common mistakes do people make?+
Off-by-one errors when strings have different lengths, forgetting to handle the case where one string is longer, and not breaking early when two mismatches are found. Also, overcomplicating with hashing when a simple pass works. Test your edge cases first.
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