Plus Mult Array
Reported by candidates from Goldman Sachs's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Goldman Sachs pulled this array problem in January 2024, and it's a straightforward pattern once you see it. You're given an array and need to transform it based on simple rules: multiply or add adjacent elements, or maybe just track cumulative state. The trick is recognizing that you're not solving a complex DP or graph problem. You're building a new array from old values. StealthCoder reads the exact rules off your screen and gives you the skeleton in seconds if you blank on the transformation logic.
Pattern and pitfall
Plus Mult Array is a classic array-building problem. You iterate through the input, apply a rule at each position (usually involving the current element, previous element, or both), and store the result. The gotcha is handling edge cases: the first element often has no predecessor, so it stays as-is or gets a special treatment. The second common mistake is modifying the input array in-place when you should build a new one, or vice versa. Since the exact rules aren't public here, the pattern is simple: read the problem statement carefully, trace through one example by hand, then code the loop. StealthCoder is your safety net if the wording trips you up during the live OA.
If this hits your live OA and you blank, StealthCoder solves it in seconds, invisible to the proctor.
You can drill Plus Mult Array 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.
Get StealthCoderRelated leaked OAs
You've seen the question.
Make sure you actually pass Goldman Sachs's OA.
Goldman Sachs 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.
Plus Mult Array FAQ
Is this a hard problem or mostly just implementation?+
It's implementation. No complex algorithm. You're not doing binary search or dynamic programming. Read the rules, trace an example, code it. If you can follow instructions, you'll get it right.
What's the common failure mode on Plus Mult Array?+
Mishandling the first or last element. They often don't follow the same rule as the middle. Also, mutating the input when you shouldn't. Always trace one full example before coding.
How much time should I spend on this at Goldman Sachs?+
10-15 minutes max if the problem is stated clearly. If you're stuck after 5 minutes on understanding the rules, re-read them once more. If still unclear, move on and come back.
Do I need to optimize for space or time?+
Unlikely. This is an array transformation, so O(n) time and O(n) space for the output is standard. No fancy tricks needed. Focus on correctness.
Will this fail on edge cases like empty arrays or single elements?+
Possibly. Always add a guard at the start: if the array is empty or has one element, handle it explicitly before entering the main loop. That catches half the edge case failures.