Find Doubles
Reported by candidates from Pure Storage's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Pure Storage's February 2024 OA includes a problem called Find Doubles, and it's a pattern-matching problem that sounds deceptively simple until you realize the edge cases will sink you. You've got an array, and you need to find or count or mark the doubles, and the trick is figuring out what "doubles" means in their specific context and how to do it efficiently without nested loops that time out. StealthCoder will catch you if you blank on the edge case handling during the live assessment.
Pattern and pitfall
Find Doubles is likely asking you to identify pairs of elements or consecutive duplicates or values that appear exactly twice. The trap is assuming one interpretation when the problem means another. If it's about finding pairs, you're probably looking at a hash-table or counting approach to track frequencies, then filter or return elements that meet the condition. If it's about marking duplicates in place, you might need two-pointers or in-place logic. The common failure is over-complicating the solution or missing boundary conditions like empty arrays, single elements, or all-unique values. In the live OA, if the problem statement is vague, you'll second-guess yourself. StealthCoder provides the solution pattern instantly so you can code with confidence and avoid the paralysis that costs time.
Drill it cold or hedge it with StealthCoder. Either way, don't walk into the OA hoping you remember the trick.
You can drill Find Doubles 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. Made for the candidate who got the OA invite this morning and has 72 hours, not six months.
Get StealthCoderThis OA pattern shows up on LeetCode as find the difference. If you have time before the OA, drill that.
You've seen the question.
Make sure you actually pass Pure Storage's OA.
Pure Storage reuses patterns across OAs. Made for the candidate who got the OA invite this morning and has 72 hours, not six months. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Find Doubles FAQ
What does 'doubles' mean in this problem?+
It almost certainly means either: values that appear exactly twice in the array, or pairs of adjacent identical elements. The problem text will clarify, but if it doesn't, ask during the OA. Hash-table counting is the safe bet for the first interpretation.
Is this an in-place problem or can I use extra space?+
If the problem doesn't say in-place, assume you can use a hash map or set. That's the fastest, safest approach. If it does say in-place, you'll need two-pointers or a marking strategy.
What's the time complexity they expect?+
O(n) with a single pass, usually. Hash-table counting is O(n) time and O(n) space. Nested loops will time out. If you can't get O(n), you've misunderstood the problem.
Are there edge cases I should handle?+
Yes. Empty array, single element, all unique elements, all duplicates, negative numbers, and zero. Test these locally first. Pure Storage likes candidates who mention edge cases before coding.
Can I solve this in 48 hours with no prior prep?+
Yes. The pattern is hash-table counting or two-pointers. Write pseudocode, trace through one example, then code. You're not inventing anything new. Confidence and clarity matter more than speed here.