Get Triplet Count
Reported by candidates from Point 72's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Point 72 asked this in April 2025, and it's exactly the kind of counting problem that looks deceptively simple until you realize the edge cases will wreck you. You're given some structure (likely an array or list), and you need to count triplets that satisfy a condition. The trap is thinking brute force is safe. It isn't. StealthCoder can spot the optimal pattern instantly if you freeze on the approach, letting you move forward without panic.
Pattern and pitfall
Triplet-counting problems almost always hinge on either a hash-table or two-pointer sweep, depending on whether the constraint is sortable. If the problem asks for triplets where values sum to a target (classic variant), you sort and use two pointers while iterating a fixed element. If it's about counting valid combinations with a specific property, hash-table precomputation beats brute force hard. The gotcha: duplicate handling. Candidates often miss that three identical elements might count as multiple triplets or zero, depending on the problem's definition. Point 72 interviews algorithmically, so expect tight constraints. The safest bet is O(n^2) with careful pruning, not O(n^3).
If this hits your live OA and you blank, StealthCoder solves it in seconds, invisible to the proctor.
You can drill Get Triplet Count 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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Get Triplet Count FAQ
What's the actual constraint I should expect for triplet problems?+
Usually array length is 100 to 5,000 elements. Brute force O(n^3) times out. You need O(n^2) with sorting or hash-table, or O(n log n) if a clever insight applies. Point 72 won't let you slide on naive.
Should I sort the array?+
If the problem allows it (no index-based requirement), sorting makes two-pointer logic bulletproof. Fix one element, then use two pointers to close the gap. This handles duplicates cleanly and runs in O(n^2).
How do I handle duplicate triplets?+
Skip duplicate values in the outer and inner loops. Once you've counted a triplet (a, b, c), don't process the same combo twice. This is where most candidates drop points.
Is this a hash-table problem?+
Not usually for counting triplets. Hash-table shines when you need to check existence fast, but triplet problems reward sorting and two-pointer logic. Keep hash-table as a backup if you can't see the sort.
How much time should I spend on this live?+
15-20 minutes to code and test. If you're stuck after 10, pivot to brute force, get it working, then optimize. Don't time-bleed on one problem.