Subarray Sum Equals K
A medium-tier problem at 45% community acceptance, tagged with Array, Hash Table, Prefix Sum. Reported in interviews at Scale AI and 33 others.
Subarray Sum Equals K is a medium-difficulty array problem that appears across 34 companies, including Meta, Tesla, PayPal, and Disney. You're given an array of integers and a target sum K. Find how many contiguous subarrays add up to exactly K. The naive brute-force approach times out on real data. Most candidates either miss the prefix sum pattern or try to brute-force all O(n²) subarrays. This is exactly the kind of problem where you blank under live-OA pressure and need a fast, invisible solution. StealthCoder surfaces the working approach in seconds if you hit this during an assessment.
Companies that ask "Subarray Sum Equals K"
Subarray Sum Equals K 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. Made for the engineer who has done the work but might still blank with a webcam pointed at him.
Get StealthCoderThe trick is prefix sums with a hash table. As you iterate through the array, track cumulative sums. For each position, ask: have I seen a prefix sum that, when subtracted from the current sum, leaves exactly K? If cumsum - prefix = K, then the subarray between them sums to K. Store every prefix sum you encounter in a hash map with its frequency. This transforms an O(n²) search into O(n) lookup. The pattern fits Array, Hash Table, and Prefix Sum topics perfectly. Most candidates waste time on nested loops or try sorting (which breaks subarray order). On a live assessment, if you can't remember the hash map trick fast enough, StealthCoder runs invisibly during screen share and gives you working code before the proctor notices the hesitation.
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Subarray Sum Equals K 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. Made for the engineer who has done the work but might still blank with a webcam pointed at him. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Subarray Sum Equals K interview FAQ
Is Subarray Sum Equals K still asked at big tech companies?+
Yes. It appears in reports from Meta, Tesla, PayPal, Disney, and 30 other companies. It's a staple medium-difficulty filter. Most candidates see it at least once in their interview cycle. The 45% acceptance rate shows it's harder than it looks on paper.
What's the key insight I'm missing if brute-force times out?+
You need prefix sums, not nested loops. Store cumulative sums in a hash map as you iterate. For each sum, check if (current_sum - K) exists in the map. That tells you how many subarrays ending here sum to K. Without this, you're stuck in O(n²).
Does this problem require sorting or rearranging the array?+
No. Sorting breaks the subarray constraint (subarrays must be contiguous in the original order). The prefix sum solution works in a single pass without touching array order. That's why it runs so fast.
How does the hash table prevent double-counting or missing subarrays?+
The map stores prefix sums you've already seen, keyed by value and counted by frequency. When you encounter a prefix sum that minus K equals an old prefix, you add that old prefix's count to your result. Each match corresponds to exactly one subarray. No duplicates because you iterate left to right once.
If I freeze on this during a live OA, how does StealthCoder help?+
StealthCoder reads the problem and constraints from your screen, generates the prefix sum hash table solution, and displays it invisibly. You paste the working code into the editor. The proctor never sees the overlay. You move on without losing time or raising red flags.
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