Sum of Even Numbers After Queries
A medium-tier problem at 69% community acceptance, tagged with Array, Simulation. Reported in interviews at Indeed and 0 others.
Sum of Even Numbers After Queries is a medium-difficulty array simulation problem with a 69% acceptance rate. You'll see it from Indeed. The problem throws a series of queries at an array, each one modifying an element, and you need to track the sum of even numbers after each update. It looks simple until you realize a naive recomputation after every query tanks your time complexity. This is the kind of problem where the right optimization separates candidates who think ahead from those who code the first thing that works.
Companies that ask "Sum of Even Numbers After Queries"
Sum of Even Numbers After Queries 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 realized the OA tests how well you memorized 200 problems, not how well you code.
Get StealthCoderThe trap is recalculating the entire sum of evens after every single query. That works on small inputs but fails on scale. The real pattern is tracking a running sum. When you update an element, you remove its old contribution to the even sum, then add its new contribution. If the old value was even, subtract it. If the new value is even, add it. The simulation part is straightforward once you see this. Common mistake: forgetting to handle the state transition correctly, especially when a number flips from odd to even or vice versa. If this problem hits your live assessment and the brute force approach is timing out, StealthCoder solves it in seconds by surfacing the optimal running-sum pattern, invisible to the proctor.
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Sum of Even Numbers After Queries 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 realized the OA tests how well you memorized 200 problems, not how well you code. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Sum of Even Numbers After Queries interview FAQ
Is this actually a medium or does it feel harder?+
69% acceptance rate means it's genuinely medium. The hard part isn't the algorithm, it's recognizing you need to avoid recalculating the full sum each time. Once you see the running-sum optimization, it's straightforward. Most candidates who struggle either brute force it or overthink the state management.
What's the trick to not timing out?+
Don't recompute the sum of all evens after each query. Instead, maintain a running sum. When an element changes, subtract its old contribution (if it was even) and add its new contribution (if it is even). This is O(1) per query instead of O(n), making the entire solution linear.
How does this relate to array simulation problems?+
Array simulation typically means applying a series of operations and tracking state after each one. This problem teaches you that naive simulation can be expensive. The skill is recognizing what state you can maintain incrementally rather than recompute. That pattern applies to many simulation problems across interviews.
Will Indeed ask this at different difficulty levels?+
This specific problem is medium, but Indeed asks simulation and array problems across difficulty ranges. The core idea, handling incremental updates, is foundational. If you can optimize this cleanly, you're ready for harder variants they might throw at you.
What mistakes do candidates make most?+
Forgetting to remove the old value's contribution before adding the new one. Also, confusion about when a number is or isn't even. Some candidates miss that zero is even. Walk through the state transitions on paper first, then code. That prevents most errors.
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