Shared Categories
Reported by candidates from TikTok's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
TikTok's August OA included Shared Categories, a problem that tests whether you can reason about set intersection and grouping under time pressure. You're given some data about items and categories, and you need to find which items share categories or group them somehow. It's the kind of problem that looks deceptively simple on read but trips you up on implementation. StealthCoder can spot the category-matching pattern in seconds and feed you a working scaffold while you stay calm.
Pattern and pitfall
Shared Categories almost certainly involves comparing category sets across items and either finding overlaps, counting shared members, or grouping by common attributes. The gotcha is usually in how you handle edge cases: empty category sets, items with no matches, or off-by-one errors in iteration. The pattern is hash-table or array-based grouping with a linear or near-linear sweep. Most candidates either over-engineer it with nested loops that timeout or under-think the grouping logic. The trick is building a map of categories to items (or vice versa) first, then querying from that lookup. During the live OA, if the exact approach isn't clicking, StealthCoder watching the input format will give you the structure you need to unblock.
If you see this problem in your OA tomorrow, the play is to recognize the pattern in 30 seconds. StealthCoder buys you that recognition.
You can drill Shared Categories 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 passed his OA cold and still thinks the filter is broken.
Get StealthCoderRelated leaked OAs
This OA pattern shows up on LeetCode as group anagrams. If you have time before the OA, drill that.
You've seen the question.
Make sure you actually pass TikTok's OA.
TikTok reuses patterns across OAs. Built by an Amazon engineer who passed his OA cold and still thinks the filter is broken. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Shared Categories FAQ
Is this a hash-table or sorting problem?+
Hash-table. Build a map of categories to items or items to categories, then iterate once to find matches. Sorting won't help here. The speed comes from O(1) lookups, not comparison-based ordering.
What's the main pitfall candidates hit?+
Nested loops checking every pair of items. That's O(n squared) and times out. You need to use the category structure as the index, not iterate pairs. Map first, query second.
How do I prep for this in 24 hours?+
Understand intersection of sets and grouping by key. Practice one hash-map grouping problem. Sketch the input format on paper. You don't need advanced knowledge, just clarity on the data structure.
Will this question ask me to optimize after the first solution?+
Possibly. Your first pass should be correct and readable. If they ask for optimization, the answer is almost always 'use a hash-map instead of nested loops,' which you should already have.
Is this question still being asked in 2024?+
Yes. TikTok reported it in August. Category matching and grouping are core interview patterns. Expect it in every batch of their OAs.