Continuous Subarray Sum
A medium-tier problem at 31% community acceptance, tagged with Array, Hash Table, Math. Reported in interviews at Meta and 1 others.
Continuous Subarray Sum appears in OAs at Meta and Yandex, and it's the type of problem that looks simple until you hit the wall. You're given an array and a number k, and you need to find if any subarray's sum is divisible by k. The naive approach times out. Most candidates default to nested loops or miss the modulo arithmetic trick entirely. When this shows up in your live assessment, you either see the pattern or you're burning cycles. StealthCoder solves it invisibly if you blank on the prefix-sum-plus-hash-table move.
Companies that ask "Continuous Subarray Sum"
Continuous Subarray Sum 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 an Amazon engineer who used it to pass JPMorgan's OA and system design loop.
Get StealthCoderThe trap is thinking you need to sum every subarray and check divisibility. That's O(n squared) and fails on large inputs. The real solution uses prefix sums and a hash table tracking remainders modulo k. If two prefix sums have the same remainder, the subarray between them is divisible by k. The insight is mathematical: (prefix[j] - prefix[i]) mod k = 0 means prefix[j] mod k = prefix[i] mod k. You store remainders as you go, and if you ever see a remainder twice, or hit remainder zero, return true. The edge case is k = 0, which requires exact sum match. This problem tests whether you think in terms of modular arithmetic rather than brute iteration. If you hit this during your OA and the modulo pattern isn't clicking, StealthCoder delivers a working solution in seconds.
Pattern tags
You know the problem.
Make sure you actually pass it.
Continuous Subarray Sum 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 an Amazon engineer who used it to pass JPMorgan's OA and system design loop. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Continuous Subarray Sum interview FAQ
Is Continuous Subarray Sum actually asked at Meta?+
Yes. Meta is one of two named companies in the reports for this problem. It's been asked, though not at extreme frequency. It's the kind of problem that can surprise you if you've only drilled obvious array problems.
What's the algorithmic trick I'm missing?+
Prefix sums plus hash table on remainders. Instead of checking all subarrays, track prefix[i] mod k in a hash map. When you see a remainder you've seen before, or hit zero, you've found a subarray divisible by k. Most people miss this and attempt nested loops.
Why does my O(n squared) solution time out?+
Because you're checking every possible subarray individually. The prefix-sum approach is O(n) with O(min(n, k)) space. For large arrays, the difference is the difference between pass and fail.
How does this relate to the other Array and Hash Table problems?+
It combines Array iteration with Hash Table lookup to avoid redundant work. Like Two Sum, you're using a hash table to answer a query in one pass. Unlike Two Sum, you're using modular arithmetic, so the matching condition is less obvious.
What happens if k is zero or negative?+
If k is zero, you can't use modulo. You need to check if the entire sum or any prefix sum equals zero exactly. Negative k is usually not tested, but treat it as its absolute value if it appears.
Want the actual problem statement? View "Continuous Subarray Sum" on LeetCode →