Identify the Non Twin Person
Reported by candidates from Cisco's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Cisco's October 2024 OA included a matching problem that sounds simple on the surface: find the person who doesn't have a twin. You're looking at what feels like a hash-table or counting problem, but the real trick is understanding what 'twin' means in their data model. Candidates often waste time overcomplicating the pairing logic. StealthCoder reads the problem as it appears on screen and flags the exact definition they're using, so you're never guessing at what counts as a match.
Pattern and pitfall
The non-twin problem typically hinges on identifying unpaired elements in a dataset. Most candidates jump to hash maps and frequency counting, which is the right direction, but miss the specific matching criteria Cisco uses. The pattern is usually counting or hash-table work: build a frequency map, iterate through, and return the element with a count of 1. The common miss is misreading the pairing definition (are twins identified by ID, by name, by some other attribute?). When you're live and brain-locked, StealthCoder shows you the solution instantly so you don't burn 15 minutes on the wrong interpretation.
StealthCoder is the hedge for the one pattern you didn't drill. It runs invisibly during the screen share.
You can drill Identify the Non Twin Person cold, or you can hedge it. StealthCoder runs invisibly during screen share and surfaces a working solution in under 2 seconds. The proctor sees the IDE. They don't see what's behind it. If you're reading this with an OA window open, you're who this was built for.
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Cisco reuses patterns across OAs. If you're reading this with an OA window open, you're who this was built for. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Identify the Non Twin Person FAQ
Is this a hash-table or counting problem?+
Both. You build a frequency map of the input, then find the key with count 1. It's straightforward once you nail the definition of what makes two people twins in Cisco's test data.
How hard is this compared to LeetCode Easy?+
It's LeetCode Easy territory, maybe slightly easier. The trick isn't the algorithm. It's reading the problem statement carefully enough to know exactly what attribute defines a twin pair.
What's the most common mistake candidates make?+
Overengineering the match logic or misunderstanding the input format. Many people assume complex pairing rules when the answer is just a straightforward frequency count with a single pass.
Can I solve this in under 5 minutes?+
Yes, if you understand the matching rule immediately. The implementation is 5-10 lines of code. The risk is spending time on wrong interpretations before you write anything.
Should I memorize a specific solution for Cisco?+
No. Memorize the counting pattern. Build the map, find the outlier. That works for any twin-matching variant Cisco throws at you.