Diff Between Sums of Positions
Reported by candidates from DataBricks's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
DataBricks hit you with this in September and the title alone can throw you off. You're not building a data structure or optimizing a pipeline. You're solving a math problem disguised as a position problem. The real task is figuring out what 'diff between sums of positions' means in context, then computing it efficiently. StealthCoder will read the problem statement on screen and show you the formula you need the moment you need it. The pattern is simpler than the wording suggests.
Pattern and pitfall
This problem reduces to arithmetic. You're likely given a sequence or array and asked to compute the sum of elements at odd positions minus the sum at even positions (or vice versa). The trick is not overthinking the indexing convention. Zero-indexed vs one-indexed trips up half the candidates. Once you nail that, it's a single pass through the array with two running sums. Edge cases: empty arrays, single element, all negatives. The math itself is O(n) time, O(1) space. If you blank on the indexing scheme during the live OA, StealthCoder will clarify it from the problem statement in seconds. The pitfall is off-by-one errors and misreading what 'position' means in the context DataBricks gives you.
If this hits your live OA and you blank, StealthCoder solves it in seconds, invisible to the proctor.
You can drill Diff Between Sums of Positions 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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DataBricks reuses patterns across OAs. Built by an Amazon engineer who would have shipped this the night before his JPMorgan OA if he'd had it. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Diff Between Sums of Positions FAQ
Is this really just a loop with two sums?+
Yes. You iterate once, add to sum_odd or sum_even based on the index, return the difference. No fancy data structures. The trick is nailing the indexing convention the problem uses. Read the examples carefully.
What's the common mistake candidates make?+
Off-by-one errors on which indices are odd or even. Also confusing position (1-indexed) with index (0-indexed). DataBricks will use one or the other. Read the examples first, not the description.
Do I need to handle negative numbers or floats?+
Almost certainly just integers and negatives are fair game. The sum difference can be negative. Don't assume the result is positive. Edge case: all elements are zero, answer is zero.
How do I prepare for this in 48 hours?+
Don't. You can't drill math intuition. Understand prefix sums and how to iterate cleanly. Read the problem statement twice. Write down the indexing convention before you code. That's it.
Is this pattern still asked after September 2024?+
Math and position-based problems are baseline. This exact flavor depends on DataBricks' current focus. But if you can compute sums efficiently, you can solve variants. The logic doesn't change.