Compact List
Reported by candidates from Cisco's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Cisco's Compact List problem hit the September 2024 rounds. It's a straightforward array manipulation question that looks deceptively simple on first read. Most candidates who blank on it aren't missing the concept; they're getting tripped up by edge cases or the exact output format Cisco expects. This is the kind of problem where StealthCoder's real-time solution feed becomes a safety net if your mind goes blank under pressure.
Pattern and pitfall
The core pattern here is array transformation or condensing. You're likely given an array with some structure (duplicates, gaps, specific ordering) and asked to produce a 'compact' version following a rule. The trick is understanding what 'compact' means in Cisco's context: it could mean removing duplicates while preserving order, collapsing consecutive elements, or rebuilding the array in a specific dense format. The pitfall is trying to compress too aggressively or mishandling the return format. Most solutions are O(n) with a single pass or two-pointer scan. If you blank during the OA, StealthCoder will show you the exact transformation pattern and help you nail the implementation.
The honest play: practice the pattern, and have StealthCoder ready for the one you didn't see coming.
You can drill Compact List 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 for the candidate who saw this exact problem leak two days before his OA and wondered if anyone had a play.
Get StealthCoderRelated leaked OAs
This OA pattern shows up on LeetCode as remove element. If you have time before the OA, drill that.
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Cisco reuses patterns across OAs. Built for the candidate who saw this exact problem leak two days before his OA and wondered if anyone had a play. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Compact List FAQ
Is this problem about removing duplicates or something else?+
It depends on how Cisco frames 'compact,' but array compaction typically involves removing or consolidating repeated or unwanted elements while maintaining relative order. Read the examples carefully; they'll tell you the exact rule. Don't assume standard duplicate removal.
Will they test edge cases like empty arrays or single elements?+
Almost certainly. Empty input, single element, all duplicates, no duplicates, and fully sorted/reverse sorted variants are standard. Code a guard at the top and trace through at least two edge cases mentally before submitting.
How much time should I budget for this in the OA?+
If it's the only problem, 15-25 minutes is realistic for coding and testing. If it's part of a multi-problem set, you should solve it in under 12 minutes. It's not meant to be a time sink; if you're stuck past 10 minutes, move on and come back.
Does the output format matter, like array vs. list notation?+
Yes. Cisco's platform will have specific output expectations: JSON array, Python list string, or plain integers separated by spaces. Copy the exact format from the example output. Format mismatches fail silently on automated tests.
Is this a common pattern I should see elsewhere?+
Compaction and in-place array modification appear across interviews (LeetCode 27, 26, 283). The core skill is two-pointer scanning and boundary management. Master that, and you'll handle Cisco's variant cleanly.