Count Three Sisters
Reported by candidates from Meta's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Meta's "Count Three Sisters" hit the OA circuit in September 2024, and candidates are blanking on what "three sisters" even means algorithmically. You're not alone. The problem likely requires you to count a specific pattern or triplet structure, possibly in an array or string. Without the exact wording, the trap is overthinking the domain. StealthCoder will read the full problem on your screen during the live OA and surface the pattern instantly if you freeze mid-approach.
Pattern and pitfall
This problem almost certainly hinges on either counting valid triplets under some constraint, or identifying three elements that satisfy a condition (order, value range, or position). The common pitfall is brute force. A triple-nested loop tanks on large inputs. The real solution likely uses hash-tables or prefix-sum logic to drop from O(n^3) to O(n) or O(n^2). The phrase "three sisters" suggests a symmetry or relationship check. Whether it's array positions, values, or a mathematical property, the trick is recognizing you can precompute or cache partial results. If you blank during the live OA, StealthCoder is your hedge to reconstruct the pattern from the problem statement alone.
The honest play: practice the pattern, and have StealthCoder ready for the one you didn't see coming.
You can drill Count Three Sisters 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.
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Count Three Sisters FAQ
What does 'three sisters' mean in this context?+
Without the full problem text, it's likely a constraint on three elements. Could be three indices forming a pattern, three values meeting a condition, or three positions satisfying a relationship. The exact meaning depends on the problem statement you see on OA day.
Is this a brute-force-then-optimize problem?+
Almost always. Triple loops are the baseline. But Meta doesn't accept O(n^3). You'll need to reduce via hashing (store counts or sums), prefix-sum (precompute ranges), or smart iteration (one or two pointers after sorting). Expect the optimal to be O(n) or O(n log n).
How much time do I have to solve this?+
Meta OAs typically give 30-45 minutes for medium problems. "Count Three Sisters" feels medium-hard. Budget 10-15 minutes for parsing the problem and walking a small example, then code the optimized version.
Should I sort the input?+
Depends on the constraints, but sorting is often a hint. If the problem cares about order or ranges, sorting + two-pointer or hash-table usually unlocks the solution. Try it if your naive approach times out.
What if I can't figure out the pattern live?+
Read the problem line by line. Trace a small example by hand. Look for the relationship between the three elements. If stuck, code a brute-force solution first, then optimize. Partial credit beats a blank submission.