Find All Good Indices
A medium-tier problem at 40% community acceptance, tagged with Array, Dynamic Programming, Prefix Sum. Reported in interviews at ByteDance and 1 others.
Find All Good Indices shows up in live OAs at ByteDance and Goldman Sachs, and it's a medium-difficulty problem with a 40% acceptance rate that trips up candidates who don't spot the prefix-sum optimization. The setup looks simple: you're scanning an array and marking indices as 'good' based on a condition tied to their neighbors. Most people write a brute-force nested loop that times out. If you freeze during the assessment and can't remember the prefix-sum trick, StealthCoder solves it invisibly in seconds, giving you a working solution to adapt.
Companies that ask "Find All Good Indices"
Find All Good Indices 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 gotcha is that the naive check for each index is O(n squared) or worse. You need prefix sums to precompute cumulative data about left and right subarrays so the 'good' condition evaluates in O(1) per index. Build a prefix array in one pass, maybe a suffix array in another, then iterate and mark indices where the condition holds. The Array and Dynamic Programming angles converge here: DP teaches you to think 'what state do I need precomputed', and prefix sums are the state machine. Candidates often skip the precomputation step because the problem reads like a simple filter. On your live OA, if the logic feels sluggish or you're nesting loops, you've missed the pattern. StealthCoder is your safety net when that moment hits.
Pattern tags
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Find All Good Indices 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.
Find All Good Indices interview FAQ
Is this problem still actively asked at FAANG?+
Yes. ByteDance and Goldman Sachs both report asking it. Acceptance sits around 40%, so it's a real filter. Companies use it to catch candidates who don't know prefix-sum acceleration or who over-engineer simple array logic.
What's the actual trick?+
Precompute prefix and suffix data in O(n) time and space so you don't recompute sums or conditions for overlapping subarrays. Each index check becomes O(1). Candidates who skip precomputation and nest loops will timeout or write unoptimized code.
How do I know when to use prefix sums?+
If your solution checks a condition for every index and that condition depends on a range sum or aggregate to the left or right, prefix sums are the answer. Watch for nested loops where the inner loop computes cumulative data. Replace it with a precomputed array.
Does this test Dynamic Programming or Array skills?+
Both. The array mechanics are trivial, but the DP insight is recognizing that you need to build state tables first. It's a DP problem dressed as an array problem. If you jump straight to iteration without precomputation, you'll fail the efficiency bar.
What's my study strategy if I haven't seen prefix sums yet?+
Drill prefix sum patterns on 3 to 5 easy problems first to build intuition. Then return to this one. On your live OA, if you blank, try writing a brute-force solution first, submit it to see if it times out, then optimize. StealthCoder gives you the optimized version instantly if you hit a wall.
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