The statement
Constraints, input and output format, and worked samples with an explanation, so you know what counts as correct before you type.
DSA practice that follows
the pattern, not a list.
352 problems in the CodeStory app, filed under the pattern that solves them and the companies that ask them. Write in C, C++, Java, Python or JavaScript, run against hidden tests, and take a hint only when you are stuck.
Free to start: 100 AI credits when you sign up and 100 every month. Practice runs never cost credits.
A list of 500 problems is not a plan.
Most students practise by scrolling a sheet. The app files every problem under the idea behind it.
A sheet tells you what to solve. It does not tell you why those problems sit together, so you finish forty of them and still freeze when the wording changes. The pattern is the part that carries over: two pointers, sliding window, monotonic stack, binary search on the answer, the half-dozen shapes of dynamic programming.
In the app, every one of the 352 problems belongs to a pattern, and every pattern has a ladder inside it: a starter problem that shows the shape plainly, then the ones that hide it. Solve the ladder and the next unseen problem in that pattern stops being a surprise.
The same 352 problems are also cut by company. 463 companies have their own set, so a week before an Amazon or a Zoho round you practise what that company actually asks instead of a generic top 100.
What one problem gives you.
The same screen a real online round gives you, minus the panic.
Run, then submit
Run on the samples or on input you make up. Submit runs the hidden tests: every problem carries cases you never see, the way a real judge works.
An honest verdict
Accepted, wrong answer, time limit, memory limit, runtime error or compile error. A wrong answer tells you it is wrong, not which line to change.
Hints, one at a time
Each problem has a ladder of hints. Take the first, try again, take the next. Hints cost no credits.
How to practise so it sticks.
The method our own batches use, and the reason the app is built this way.
- Read the idea firstOpen the free guide for the pattern, or watch it move in the visualiser. Ten minutes of understanding saves an hour of guessing.
- Solve the starter, then the coreOne problem where the pattern is obvious, then two where it is buried. If the second one takes more than 40 minutes, go back to the idea.
- Say the approach out loudBefore you type, say the plan in one sentence: what you keep, what you throw away, and why it is faster than brute force.
- Then take the company setA week before a round, switch from patterns to that company's set and time yourself. The panic you feel there is cheaper than the panic in the round.
Where to go next.
The pages students open after this one.
Questions about dsa practice.
Still not sure? Start free, or a mentor answers on a call.
Start freeIs DSA practice on CodeStory free?
Yes, to start. You get 100 AI credits at sign-up and 100 every month, and running or submitting a solution never costs credits. No card to begin.
Which languages can I write in?
C, C++, Java, Python and JavaScript. Each language has its own time limit on every problem, so a slower language is not punished for being slower.
How many problems are there, and how are they organised?
352 problems in the judge, filed under 71 patterns, and cut again into sets for 463 companies.
Is this the same as the paid batch?
No. The app is practice you run on your own. The online batch adds live classes, a mentor who reviews your code and scored mock rounds, and it includes the app's Pro plan while the batch runs.
Where do I start if I have never done DSA?
Start with the free guides on arrays, hash tables and Big O, then the starter problem in each pattern. The app orders them for you.
Not sure where to start? A mentor calls you, free.
Tell us who you are. On the call we help you pick the right batch.
- 1We check your level, from never coded to ready for interviews.
- 2We suggest online or campus, and a batch timing that fits your day.
- 3You decide. No pressure, no payment on the call.