Phone Album
Reported by candidates from FactSet's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
FactSet asked this in September 2024, and it's a deceptively simple problem that trips up candidates who don't see the constraint early. You're organizing photos on a phone, probably grouped by album or timestamp, and the question is asking you to solve it efficiently. The real catch isn't the algorithm, it's recognizing what you're actually optimizing for. If you blank on the structure during the OA, StealthCoder can read the exact problem and surface the pattern in seconds, so you stay on pace.
Pattern and pitfall
Without the full problem text, the pattern here likely hinges on either grouping logic (hash table or array index tricks) or interval merging if albums span date ranges. FactSet's OA problems tend to reward clean enumeration over fancy algorithms. The trick is probably that a naive nested loop works but wastes time, while a single pass with a map or sorted grouping runs in linear or n-log-n time. Common pitfall: over-engineering with a graph or segment tree when the problem just wants you to traverse phone storage smartly. If you're stuck mid-OA and can't recall the grouping strategy, StealthCoder reads the problem constraints and gives you the exact approach to code.
If this hits your live OA and you blank, StealthCoder solves it in seconds, invisible to the proctor.
You can drill Phone Album 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. Built by an Amazon engineer who would have shipped this the night before his JPMorgan OA if he'd had it.
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FactSet reuses patterns across OAs. Built by an Amazon engineer who would have shipped this the night before his JPMorgan OA if he'd had it. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Phone Album FAQ
Is this a sorting or grouping problem?+
Likely both. You'll probably sort photos by some key (date, album name) then group them together. The efficiency win comes from doing this in a single pass, not re-scanning. If you see 'album' or 'collection', think hash table or sorted array.
Will they ask for time and space complexity?+
Almost certainly. Aim for O(n log n) time if sorting is involved, O(n) for a single grouping pass. Space is usually O(n) for the output. FactSet cares about clarity and efficiency, not tricks.
How do I prepare for this in 24 hours?+
Know your groupby patterns: hash tables, sorting, and two-pass algorithms. Code a simple 'group array of objects by key' solution in your language. That template solves 80% of FactSet's OA problems.
What's the gotcha that fails submissions?+
Off-by-one in grouping boundaries or forgetting to handle edge cases like empty albums or single-photo groups. Always test with a three-album, seven-photo example before submitting.
Is this hard for FactSet's bar?+
No. It's medium difficulty, maybe easier. FactSet wants to see clean code and correct output. If you over-complicate it, you waste time. Simple enumeration with proper grouping wins.