Minimum Penalty for a Shop
A medium-tier problem at 68% community acceptance, tagged with String, Prefix Sum. Reported in interviews at Stripe and 0 others.
You're facing a string problem that looks deceptively simple until you realize the naive approach will time out. Minimum Penalty for a Shop has a 67% acceptance rate, which means a third of candidates who attempt it during an OA blank on the optimization. Stripe asks this one. The trick isn't hard once you see it, but if you freeze during the live assessment and start iterating through every possible split point with a nested loop, you'll run out of time. StealthCoder surfaces the pattern instantly if you hit the wall, invisible to the proctor. The real work happens in recognizing when prefix sums transform an O(n^2) mess into O(n) clarity.
Companies that ask "Minimum Penalty for a Shop"
Minimum Penalty for a Shop is the kind of problem that decides whether you pass. StealthCoder reads the problem on screen and surfaces a working solution in under 2 seconds. Invisible to screen share. The proctor sees nothing. Built by a senior engineer who knows the OA is theater. This is the script.
Get StealthCoderThe problem gives you a string of Y's and N's and asks you to find a split point that minimizes a penalty. Most candidates intuitively loop through every position, then count Y's on the left and N's on the right for each split. That's O(n^2) and it dies on large inputs. The insight is a prefix sum: precompute how many Y's exist up to each position, then iterate once, calculating the penalty in constant time per position. You'll also need to count total N's upfront. The gotcha is handling the penalty formula correctly and remembering to check the boundary cases (split at position 0 and at the end). This pattern, where you collapse nested loops using cumulative state, appears across interview problems. If you haven't drilled prefix sums recently and this hits your OA cold, StealthCoder solves it in seconds without the proctor catching the overlay.
Pattern tags
You know the problem.
Make sure you actually pass it.
Minimum Penalty for a Shop recycles across companies for a reason. It's medium-tier, and most candidates blank under the timer. StealthCoder is the hedge: an AI overlay invisible during screen share. It reads the problem and surfaces a working solution in under 2 seconds. Built by a senior engineer who knows the OA is theater. This is the script. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Minimum Penalty for a Shop interview FAQ
Is this problem actually asked at companies like Stripe?+
Yes. Stripe is listed as the reported asker. That said, one company report is lower frequency than problems appearing across ten plus companies. But if you're interviewing there, treat it as a real possibility.
What's the core trick I'm missing?+
Prefix sums. Precompute cumulative Y counts from the left. Loop once, tracking N's as you go. For each split, penalty is O(1) instead of recounting. That collapses O(n^2) to O(n).
How does this relate to the String and Prefix Sum topics?+
You iterate a string character by character, which is the String part. Prefix Sum is the algorithmic pattern that makes it efficient. Both topics live in the same solution. Master both to nail the optimization.
Will my brute force pass some test cases?+
Likely. Small inputs (n under 1000) may tolerate O(n^2). But the OA usually includes at least one large input that forces you to optimize. You'll hit a time limit exceeded.
How do I make sure I handle edge cases?+
Test split at position 0 (all N penalty on right), split at string length (all Y penalty on left), and a middle case. Off-by-one errors are common when building prefix arrays. Write out a manual trace on a small example first.
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