XOR Queries of a Subarray
A medium-tier problem at 78% community acceptance, tagged with Array, Bit Manipulation, Prefix Sum. Reported in interviews at Airtel and 0 others.
XOR Queries of a Subarray is a medium-difficulty bit manipulation problem that combines prefix sums with XOR logic. You're given an array and must answer multiple queries about the XOR of elements within specific ranges. It's asked at companies like Airtel and accepted by 78% of candidates, but that acceptance rate hides a critical trick: most people solve it the slow way first, then realize they need preprocessing. If this problem hits your live assessment and you freeze on the optimization, StealthCoder surfaces the prefix-XOR solution invisibly so you're not burning time on a brute force.
Companies that ask "XOR Queries of a Subarray"
XOR Queries of a Subarray 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 by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know.
Get StealthCoderThe naive approach computes XOR for each query by iterating the range every time, which fails under time pressure. The pattern is prefix sums, but applied to XOR instead of addition. Build a prefix array where prefix[i] is the XOR of all elements from index 0 to i-1. Then any subarray XOR from index left to right equals prefix[right+1] XOR prefix[left]. The math works because XOR is self-inverse: a XOR a equals 0. The trap is either forgetting the offset or not recognizing that XOR obeys prefix logic the same way addition does. Once you see it, it's clean: O(n) preprocessing, O(1) per query. This is exactly where candidates blank during screen share and where StealthCoder gets you unstuck.
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XOR Queries of a Subarray 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 by a working FAANG engineer who treats the OA the way companies treat hiring: as a game with rules you should know. Works on HackerRank, CodeSignal, CoderPad, and Karat.
XOR Queries of a Subarray interview FAQ
Why does XOR work with prefix arrays like addition does?+
XOR is self-inverse and associative. If prefix[i] is XOR of elements 0 to i-1, then subarray XOR from left to right equals prefix[right+1] XOR prefix[left]. The XOR operation cancels out all elements before left, leaving only the target range.
What's the most common mistake on this problem?+
Off-by-one errors in the prefix array indexing. Candidates either forget to initialize prefix[0] as 0 or mix up inclusive/exclusive bounds. Double-check your indices when computing the range XOR.
Is this still asked at FAANG or major tech companies?+
It's confirmed at Airtel. Bit manipulation plus prefix sums is a classic combo, so expect variations of this pattern. It's not exotic, but it tests both optimization and pattern recognition.
How hard is the XOR logic itself compared to the prefix trick?+
The XOR logic is trivial once you know the trick. The hard part is recognizing that prefix optimization applies. Many candidates get stuck on the brute force and don't see the O(n) solution under time pressure.
Can I solve this without prefix sums?+
Technically yes, but it's slow. Brute force gives O(n*m) where m is the number of queries. The prefix approach is O(n+m). In a live assessment, the brute force will timeout on large inputs, so the prefix trick isn't optional.
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