Math problems,
and the tell.
The input is numbers and the answer needs a property of them: digits, factors, powers, remainders. 271 problems in the catalogue carry this tag, from first-week easy to interview hard.
Free to start. Running and submitting a solution never costs credits.
How the pattern actually works.
One mechanism, and the mistake that costs people the problem.
The tell. The input is numbers and the answer needs a property of them: digits, factors, powers, remainders.
The mechanism. These are rarely about clever loops. They are about noticing the identity that collapses the work: a modulo rule, a parity argument, a formula for the sum, or a bound that makes brute force fine.
What goes wrong. Overflow, and negative numbers under a modulo. Both pass the sample and fail the hidden tests.
The ones asked most often.
By how often the catalogue records them being set, not by our opinion.
- Insert Delete GetRandom O(1)Mediumasked at 40 companies
- Rotate ImageMediumasked at 33 companies
- Count All Valid Pickup and Delivery OptionsHardasked at 2 companies
- Maximum Number of Balls in a BoxEasyasked at 2 companies
- Count Strictly Increasing SubarraysMediumasked at 2 companies
- Sell Diminishing-Valued Colored BallsMediumasked at 2 companies
- Construct the Longest New StringMediumasked at 2 companies
- The Number of Good SubsetsHardasked at 2 companies
- Airplane Seat Assignment ProbabilityMediumasked at 2 companies
- Broken CalculatorMediumasked at 2 companies
Read it, watch it, then solve it.
The order that makes a pattern stick.
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About math problems.
Free to start, no card.
Start practisingHow do I know a problem is a math problem?
The input is numbers and the answer needs a property of them: digits, factors, powers, remainders.
How many math problems should I solve?
Enough to stop needing the hint, which is usually ten to fifteen across the levels, not the whole list. The catalogue tags 271, split roughly 54 easy, 97 medium and 49 hard in the sample we show, so work up rather than across.
What goes wrong most often in math problems?
Overflow, and negative numbers under a modulo. Both pass the sample and fail the hidden tests.
Is practising by pattern better than a problem sheet?
A sheet tells you what to solve. A pattern tells you why those problems sit together, which is the part that carries over to the problem you have not seen. That is why the app files every problem under its pattern.