Minimize Multiples of Three
Reported by candidates from Toshiba's online assessment. Pattern, common pitfall, and the honest play if you blank under the timer.
Toshiba's September OA included a number-theory problem asking you to minimize multiples of three. You're staring at a problem with no obvious greedy move, and the math isn't clicking. This is the kind of question that trips up candidates who think brute force first. The real insight is about modular arithmetic and how remainders chain together. StealthCoder can spot the pattern in seconds if you blank on the approach during the live assessment.
Pattern and pitfall
The trick here is recognizing that you're not just minimizing a value, you're optimizing under a modular constraint. The problem likely gives you operations (add, subtract, multiply, or digit removal) and asks for the smallest result divisible by 3. The standard move: sort numbers by their remainder mod 3, then figure out which digits or operations get you to remainder 0. Many candidates waste time trying all combinations. The pattern is math combined with greedy selection of digits or operations. StealthCoder reads the problem text and highlights the modular constraint immediately, so you don't miss the structural insight under pressure.
Drill it cold or hedge it with StealthCoder. Either way, don't walk into the OA hoping you remember the trick.
You can drill Minimize Multiples of Three cold, or you can hedge it. StealthCoder runs invisibly during screen share and surfaces a working solution in under 2 seconds. The proctor sees the IDE. They don't see what's behind it. Made for the candidate who got the OA invite this morning and has 72 hours, not six months.
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Toshiba reuses patterns across OAs. Made for the candidate who got the OA invite this morning and has 72 hours, not six months. Works on HackerRank, CodeSignal, CoderPad, and Karat.
Minimize Multiples of Three FAQ
What's the actual constraint here? Do I minimize the number itself or the number of operations?+
Without the full problem text, assume you're minimizing the final numeric result while ensuring it's divisible by 3. The operations (digit removal, arithmetic) are the mechanism. The goal is always the smallest outcome that meets the divisibility rule.
Is this a digit DP problem or straight math?+
Likely straight modular arithmetic with greedy selection. If the problem involves building numbers digit-by-digit, DP may appear. But most Toshiba variants of this are solvable by understanding which digits/operations preserve or reset mod 3 state.
How do I check divisibility by 3 efficiently?+
Sum of digits mod 3 equals the number mod 3. So track digit sums, not the number itself. This cuts computation dramatically and is the key insight most candidates miss.
Do I need to handle negatives or just positive integers?+
Assume positive unless the problem states otherwise. Toshiba's number-theory OAs typically stay in positive domain to avoid edge-case confusion.
Can I solve this in 48 hours if I haven't seen it before?+
Yes. Spend 20 minutes on the math property (divisibility rule for 3), 20 on a brute-force baseline, then optimize. The insight lands fast once you test small examples. Don't overthink.