Prime In Diagonal
A easy-tier problem at 36% community acceptance, tagged with Array, Math, Matrix. Reported in interviews at IBM and 0 others.
Prime in Diagonal is an easy problem that's been asked at IBM and appears to target candidates who can spot patterns in matrices. The 36% acceptance rate is misleading for an easy problem, which suggests the trick isn't obvious on first read. You're likely working with a 2D array and checking diagonals for prime numbers, but the specific constraint or edge case trips people up. If this hits your live OA and you misread what the problem's actually asking, StealthCoder surfaces a working solution in seconds while the proctor sees nothing.
Companies that ask "Prime In Diagonal"
Prime In Diagonal 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 core challenge here is extracting diagonal values from a matrix and identifying which are prime. The obvious approach is straightforward: iterate through diagonals, check each number against a prime test. Where candidates stumble is determining which diagonals matter (main diagonal only, all diagonals, specific direction), or handling edge cases like 1 and negative numbers in the prime check. The Number Theory component means your isPrime() function has to be clean and correct. The low acceptance rate for an easy problem signals that most people either misread the diagonal extraction logic or implement a prime checker that fails on boundary cases. This is the kind of problem that's trivial once you see it, brutal when you guess wrong under time pressure.
Pattern tags
You know the problem.
Make sure you actually pass it.
Prime In Diagonal recycles across companies for a reason. It's easy-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.
Prime In Diagonal interview FAQ
Why is acceptance so low for an easy problem?+
The problem likely hinges on a subtle constraint about which diagonals to check or what counts as prime. Candidates either misread the diagonal logic or write a faulty prime checker that fails on edge cases like 1. Once you nail the exact requirement and implement clean prime logic, it's straightforward.
Is this still asked at FAANG or just IBM?+
Our data shows IBM as the only company reporting this problem. It may appear elsewhere, but it's not a high-frequency ask across major tech companies. It's a solid screening problem for roles that care about math fundamentals and array manipulation.
What's the trick to not messing up the prime check?+
Remember 1 is not prime, 2 is prime, and negatives are never prime. Use a simple trial division loop up to sqrt(n). Most failures come from off-by-one errors in the loop bounds or forgetting to handle edge cases before the main logic.
How does Matrix relate to the other topics here?+
The problem lives in a 2D array (Matrix), you navigate it (Array), you test each value for primality (Number Theory), and you may need modular arithmetic or divisibility checks (Math). All four topics work together to solve one coherent problem.
Should I memorize primes or compute them?+
For small matrices, compute primes on the fly with an isPrime function. If the problem involves a large range or multiple queries, precompute using a sieve. The input data will guide your choice, but a clean is-prime checker handles most cases fast enough.
Want the actual problem statement? View "Prime In Diagonal" on LeetCode →