Number of Subarrays With AND Value of K
A hard-tier problem at 34% community acceptance, tagged with Array, Binary Search, Bit Manipulation. Reported in interviews at DE Shaw and 0 others.
You've got a hard problem asking you to count subarrays where the bitwise AND equals exactly K. DE Shaw has asked this one. With a 34% acceptance rate, most candidates either miss the bit manipulation insight or brute force into timeout. The trick isn't obvious: AND operations on subarrays have a special monotonicity property that kills naive approaches. If you hit this during a live OA and your first instinct is nested loops, StealthCoder surfaces a working solution in seconds while you stay invisible to the proctor.
Companies that ask "Number of Subarrays With AND Value of K"
Number of Subarrays With AND Value of 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 core pattern: as you extend a subarray to the right, the AND value either stays the same or decreases (never increases). This means for each right endpoint, there are only O(log n) distinct AND values to track, not O(n). Most candidates either iterate all subarrays (exponential timeout) or miscalculate which subarrays produce AND equal to K. You need to use a map to store each distinct AND value and its count as you slide right, updating it by iterating through previous values and computing new ANDs. Segment trees and binary search become relevant only for advanced optimizations or specific constraints. The real edge comes from understanding that the number of unique AND prefixes ending at position i is bounded by the number of bits (roughly 32 for ints). StealthCoder handles the state-transition logic that catches most candidates off guard in real time.
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Number of Subarrays With AND Value of K recycles across companies for a reason. It's hard-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.
Number of Subarrays With AND Value of K interview FAQ
How do you avoid timeout on this problem?+
The key insight is that AND values decrease monotonically as you extend right. For each position, track only the distinct AND values reachable from all previous positions, not all subarrays. Since AND decreases with each new element, there are at most log(n) unique values per position. This reduces complexity from O(n^3) to O(n log n).
Is this still asked at major tech firms?+
It's reported from DE Shaw. Hard bit manipulation problems like this aren't as common as medium-difficulty array questions, but they do appear in specialized trading and systems roles where bit-level thinking matters. It's a sieve to separate strong candidates.
What's the most common mistake candidates make?+
Trying to check every subarray directly (double or triple loop). That's O(n^2) or worse, and often times out. The second mistake is forgetting that AND only decreases or stays the same, so you can prune your search space. Understanding monotonicity is the actual problem.
Do I need to know segment trees for this?+
Not for a correct solution. Segment trees are listed as a topic but not required. The monotonicity trick with a hash map is sufficient and faster in practice. Segment trees become relevant only if you're optimizing for very large arrays or multiple queries.
How does bit manipulation connect to the other topics?+
Binary search and segment trees are optional optimizations for specific constraints. The core is bit manipulation: understanding that AND is monotonic and that the number of distinct AND values is bounded. Array iteration and the map update are the real mechanics.
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