Brainstellar is a free, community-built collection of probability and logic puzzles, graded from easy to hard, that has been a rite of passage for quant aspirants for years. It is charming, it is free, and several of its puzzles are genuine interview classics. QuantVault covers the same puzzle territory as one topic inside a structured platform — with full worked solutions, firm mapping, and the rest of the interview loop attached. Here is the honest split.
What Brainstellar is best at
- A curated classic-puzzle canon. The collection concentrates the puzzles that made the rounds at trading desks and IIT/olympiad circles — many are the ur-versions of questions still asked today.
- Difficulty grading that means something. The easy/medium/hard split is honest; the hard ones are genuinely hard.
- Completely free. No account, no paywall, no upsell.
What QuantVault is best at
- Worked solutions, not just answers. Brainstellar's answers are often a hint or a terse sketch — great for strong solvers, brutal when you are stuck. Every QuantVault problem carries a full step-by-step solution, hints, and an intuition section explaining why the framing works.
- Firm context. Knowing a puzzle is fun; knowing Jane Street asks expectation-style versions of it in round one is prep. Problems map to the 55+ firm funnels where they actually appear.
- The rest of the loop. OA simulations, mental-math formats, trading games, statistics and stochastic-process problems, coding — the stages a puzzle site does not touch.
- Feedback and targeting. An Elo-rated daily warmup finds your weak topics and feeds you the next problem worth doing, instead of you browsing a static list.
Side-by-side comparison
| Dimension | QuantVault | Brainstellar |
|---|---|---|
| Problem bank | 2,800+ across all quant topics, ~400 free | A few hundred classic puzzles |
| Solutions | Full worked solutions + hints + intuition | Brief answers / hint-style sketches |
| Firm-specific prep | 55+ firm funnels, OA sims, games | None |
| Adaptivity | Elo-rated warmup targets weak topics | Static list |
| Coverage beyond puzzles | Probability, stats, ML, coding, market-making | Puzzles only |
| Price | Free tier + Pro | Free |
Which one should you use?
If you are early in prep and love puzzles, Brainstellar is a lovely free on-ramp — work through the easy and medium tiers for pure enjoyment and pattern exposure. When interviews get real, switch your reps to where the feedback is: full solutions when you are stuck, firm funnels that tell you which puzzle families your target firm actually asks, and the OA/game formats that decide the early rounds. Treat Brainstellar as the appetizer, structured prep as the training plan.
Start practicing on QuantVault
The brain-teaser bank and probability bank cover the same classic territory with full worked solutions — about 400 problems free, next to the firm funnels and trading games.
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Frequently asked questions
Is Brainstellar good for quant interview prep?
Yes, as a free source of classic probability and logic puzzles — several are genuine interview ancestors. Its limits: answers are terse (often hint-level), there is no firm mapping, and it covers only puzzles — no statistics, OA formats, coding, or market-making.
What is the main difference between Brainstellar and QuantVault?
Brainstellar is a free static puzzle list with brief answers. QuantVault is a structured platform: 2,800+ problems with full worked solutions and intuition, firm-by-firm interview funnels, timed OA simulations, trading games, and an adaptive warmup that targets your weak topics.
Are Brainstellar puzzles still asked in interviews?
Variants of them, yes — especially the probability and expectation classics. Interviewers usually dress them in new numbers or a trading context, which is why practicing them with full solutions and firm context transfers better than memorizing the originals.
Is there a free alternative to Brainstellar with fuller solutions?
QuantVault's free tier (~400 problems) covers the same brain-teaser and probability ground with complete step-by-step solutions, hints, and intuition sections, no card required.
Practice the real thing
QuantVault has 2,800+ quant interview problems with full solutions, intuition, and hints, firm-by-firm interview funnels, and an auto-graded coding judge. Start free.