Maximum Number of Balls in a Box
A easy-tier problem at 74% community acceptance, tagged with Hash Table, Math, Counting. Reported in interviews at AppDynamics and 1 others.
Maximum Number of Balls in a Box is one of those deceptively simple problems that tests whether you actually understand what you're counting. With a 74% acceptance rate, it looks easy on paper. The catch: most candidates misread the constraint or brute-force when a hash table observation cuts the work in half. AppDynamics and Lucid have both asked it. If you hit this during your assessment and freeze on what "box" even means in context, StealthCoder runs invisible during screen share and hands you the working solution in seconds.
Companies that ask "Maximum Number of Balls in a Box"
Maximum Number of Balls in a Box 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 used it to pass JPMorgan's OA and system design loop.
Get StealthCoderThe problem hinges on digit sum grouping. You're not sorting balls or simulating a physical box. Instead, you map each ball number to the sum of its digits, then count how many balls fall into each digit-sum bucket. The maximum count across all buckets is your answer. The math topic tag is key: recognizing that digit sum is the grouping function, not the answer itself. A hash table holds the counts. The pitfall is overcomplicating the ball-to-box mapping or trying to simulate placement. Once you see the pattern, it's a straightforward hash table scan. If you're prepping and this pattern doesn't click immediately, StealthCoder is your safety net on the live OA.
Pattern tags
You know the problem.
Make sure you actually pass it.
Maximum Number of Balls in a Box 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 used it to pass JPMorgan's OA and system design loop. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Maximum Number of Balls in a Box interview FAQ
Is this actually an Easy problem or will it trick me in an interview?+
The 74% acceptance rate confirms it's genuinely easy once you see the digit-sum grouping trick. The risk is misunderstanding what a 'box' represents. If you test a few examples by hand, the pattern emerges fast. It's not a gotcha if you read carefully.
What makes this a hash table problem and not just counting?+
You need to track the count for each unique digit sum. A hash table lets you store and retrieve these counts in O(1) time. Without it, you'd either sort or scan repeatedly. The hash table is the efficient data structure, not the core insight.
Do I need to know number theory or advanced math?+
No. Digit sum is basic arithmetic. The 'Math' topic tag refers to the digit-sum formula itself, which is just summing the digits of a number. No modular arithmetic, primes, or factorization needed.
Is this still asked at AppDynamics or Lucid in real interviews?+
Both companies are in the input data as having asked it. Smaller company asks often persist longer than FAANG problems because the pool of candidates is different. Don't skip it even if you're targeting bigger names.
What's the fastest way to solve this if I blank on the approach?+
Work through one example by hand: assign each ball a digit sum, count them in a hash table, return the max. That 2-minute manual trace usually unlocks the pattern. If it doesn't, you have StealthCoder running invisibly to pull you through.
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