Check If It Is a Good Array
A hard-tier problem at 61% community acceptance, tagged with Array, Math, Number Theory. Reported in interviews at Dropbox and 2 others.
You've hit a problem that catches most candidates off guard: Check If It Is a Good Array. It's been asked at Dropbox, Nokia, and Jump Trading. On the surface it looks like a straightforward array validation. But the trick lives in number theory, not iteration. The acceptance rate hovers around 61%, which means nearly 40% of people solve it wrong or run out of time chasing the brute-force path. If this problem lands in your live OA and you can't see the mathematical pattern, StealthCoder runs invisibly and surfaces the working solution in seconds.
Companies that ask "Check If It Is a Good Array"
Check If It Is a Good Array 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 gotcha here is that this problem isn't about iterating through the array smartly. It's about recognizing a mathematical property that determines validity without checking every combination. Most candidates start by building subsequences or simulating operations, which either times out or misses the actual constraint. The real insight comes from number theory: specifically, understanding what GCD and linear combinations tell you about which numbers you can construct. The problem tests whether you can think beyond data structures into pure math. When you're stuck in the OA, that's the wall most people hit. StealthCoder bridges that gap by showing you the mathematical check you're supposed to recognize, letting you code the solution with confidence even if the theory didn't click during prep.
Pattern tags
You know the problem.
Make sure you actually pass it.
Check If It Is a Good Array 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. 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.
Check If It Is a Good Array interview FAQ
Is this really a HARD problem or does it just feel that way?+
It's legitimately hard because it requires number-theory insight, not just coding skill. The 61% acceptance rate reflects that many strong engineers miss the mathematical pattern and waste time on simulation approaches. Difficulty here comes from the thinking leap, not implementation complexity.
Do I need to know advanced number theory to solve this?+
You need to know GCD (greatest common divisor) and Bezout's identity, but not at a research level. If you haven't studied that in years, it won't be obvious. That's exactly why StealthCoder exists: to catch the pattern you haven't drilled and show you the clean solution on the fly.
Is this still asked at FAANG or bigger tech companies?+
It's been asked at Dropbox, Nokia, and Jump Trading. Those are solid signal: companies that value problem-solving depth. It's in the mid-to-hard rotation at firms that care about algorithmic thinking beyond the obvious.
What's the relationship between Array, Math, and Number Theory topics here?+
The array is the input container, but the actual work is math and number theory. You're not optimizing traversal or using clever data structures. You're finding a mathematical property that determines if the array is 'good'. The topics tell you where your brain needs to be.
What's the most common wrong approach?+
Trying to simulate the operations or build all possible subsequences. That feels intuitive but either times out or fails edge cases. The right approach is a single mathematical check based on GCD properties. That's the gap between getting stuck and solving it cleanly.
Want the actual problem statement? View "Check If It Is a Good Array" on LeetCode →