Backtracking problems,
and the tell.
The problem asks for all the arrangements, combinations or placements that work. 63 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 problem asks for all the arrangements, combinations or placements that work.
The mechanism. Choose, recurse, then undo the choice. Prune the moment a partial answer cannot possibly finish, which is what separates a few thousand calls from a few billion.
What goes wrong. Forgetting to undo. State left behind after a branch returns silently corrupts every branch after it.
The ones asked most often.
By how often the catalogue records them being set, not by our opinion.
- Synonymous SentencesMediumasked at 3 companies
- Additive NumberMediumasked at 1 companies
- Minimum Time to Break Locks IMediumasked at 1 companies
- Maximum Points in an Archery CompetitionMediumasked at 1 companies
- Largest Time for Given DigitsMediumasked at 1 companies
- Maximum Good People Based on StatementsHardasked at 1 companies
- Letter Case PermutationMediumasked at 1 companies
- Optimal Account BalancingHardasked at 5 companies
- Maximize Score After N OperationsHardasked at 1 companies
- Next Greater Numerically Balanced NumberMediumasked at 1 companies
Read it, watch it, then solve it.
The order that makes a pattern stick.
Everything in the app, in one place.
Practice, interviews and the tools, all free to start. Swipe to see the rest.
DSA practice
Problems filed under the pattern that solves them, not a sheet.
352 problemsOpenCompany sets
Practise what one company actually asks, the week before the round.
463 companiesOpenCoding interview
Pick the role, write in a real editor, and answer while you type.
scored reportOpenMock interviews, spoken
You answer out loud, it follows up on what you said.
36 topicsOpenDatabase round
DBMS asked the way a panel asks it: indexes, joins, normal forms.
in Core CSOpenOOP round
Inheritance, polymorphism and the follow-up you never rehearse.
in Core CSOpenSystem design
How real systems are built, from the primitives to the AI stack.
27 chaptersOpenSQL practice
Real schemas, your query, the rows it returns, and an honest verdict.
39 questionsOpenAptitude
Quant, logical, verbal, DI and technical, timed like the real test.
280 questionsOpenOnline assessment
A clock, marks per question and hidden tests, like a company's judge.
37 papersOpenAlgorithm visualiser
Watch it run on your own input, one step at a time.
26 algorithmsOpenAI that helps, not solves
Hints one at a time, AI review before a mentor reads it.
100 free creditsOpenResume builder
Build it inside the app, next to the work you practised.
in the appOpenProgress and readiness
One score, and the axis you are weakest on.
tracked dailyOpen
Free to start: 100 AI credits when you sign up and 100 every month. Start free in the app
About backtracking problems.
Free to start, no card.
Start practisingHow do I know a problem is a backtracking problem?
The problem asks for all the arrangements, combinations or placements that work.
How many backtracking 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 63, split roughly 1 easy, 41 medium and 21 hard in the sample we show, so work up rather than across.
What goes wrong most often in backtracking problems?
Forgetting to undo. State left behind after a branch returns silently corrupts every branch after it.
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.