macOSv0.19.4
Practice coding.
Keep everything local.
Solve LeetCode-style problems in JavaScript, TypeScript or Python, then build engineering projects scored on concurrency, latency and code quality. Everything runs on your machine.
Free & open sourcemacOSWindowsLinux
AlgoLocal
▶ RunTypeScript⌄
Two SumEasy · Array · Hash table
Valid ParenthesesEasy · String · Stack
Merge Two Sorted ListsEasy · Linked list
Binary Tree InorderMedium · Tree · Stack
Top K FrequentMedium · Heap
28 problems
TS two-sum.ts ×
1 function twoSum(nums: number[], target: number) {
2 const map = new Map<number, number>();
3
4 for (let i = 0; i < nums.length; i++) {
5 const complement = target - nums[i];
6 if (map.has(complement)) {
7 return [map.get(complement)!, i];
8 }
9 map.set(nums[i], i);
10 }
11 return [];
12 }TestsConsole
Test case 1✓
Test case 2✓
Test case 3✓
nums = [2,7,11,15], target = 9
Output [0,1] PassedHow a practice session works.
Two ways to practice: algorithm problems, or engineering projects.
- 01
Pick a problem or a project
LeetCode-style problems by topic and difficulty, or a multi-stage engineering project.
- 02
Write code in a real editor
The Monaco editor, with a full file tree on engineering projects.
- 03
Run the tests locally
WebAssembly runs every test case on your machine.
- 04
See how it scored
Test results for problems; concurrency, latency and code quality for projects.
function solve(input) {
// your approach stays here
return result;
}
// your approach stays here
return result;
}
Test case 1Passed ✓
Test case 2Passed ✓
Solved12/28
Keep practicing.
Past 12 weeks
Less More
Engineering projects,
built stage by stage.
Each project is a multi-file workspace you clear one stage at a time. Hidden tests check that it works, measured gates check how it behaves — peak concurrency, latency, retries, duplicate calls — and static analysis reviews the code itself.
- Resilient fetch pipelineBounded concurrency, backoff, single-flight caching, cancellation
- Event-driven order pipelineEvent bus, onion middleware, idempotency, dead letter queue
- Resilient API gatewayToken bucket, circuit breaker, timeout budgets
1. Contract2. Bounded concurrency3. Retry4. Caching5. Ship it
contract.tsfetcher.tspool.ts
export async function mapWithConcurrency(items, limit, worker) {
const results = new Array(items.length);
const size = Math.min(limit, items.length);
// one pull-based worker per slot
await Promise.all(runners);
return results;
}
const results = new Array(items.length);
const size = Math.min(limit, items.length);
// one pull-based worker per slot
await Promise.all(runners);
return results;
}
STAGE PASSED10/10 cases100
- Peak concurrency at most 44 / 4
- Never throttled by upstream0 / 0
- 12 requests within 300ms300ms / 300ms
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Several approaches, with their complexity trade-offs.
AI when you want it.
Focus when you don’t.
Generate a problem, ask for a hint, or compare solutions. Connect DeepSeek, OpenAI, Claude, Qwen, any OpenAI-compatible endpoint local or remote, or run it all on your own machine with Ollama or LM Studio — or skip AI entirely.
Set up an AI provider →Current problem
Two Sum
Return the indices of two numbers that add up to the target.
const complement = target - nums[i];Your question
Give me a hint without revealing the full answer.
Think about what information you need to remember as you scan the array once.
Try this nextStore each value with its index, then look for its complement.
Three languages.
One local runtime.
JavaScriptNative browser execution
TypeScriptReal-time transpilation
PythonCPython through Pyodide
No account. No telemetry. Your attempts stay on your machine.
Download AlgoLocal.
Free and open source, for macOS, Windows and Linux.
Windowsv0.19.4
Linuxv0.19.4
First launch on macOS. These builds are signed ad-hoc rather than with an Apple Developer ID, so macOS will say it cannot verify the app.
- Open AlgoLocal from Applications and click Done on the warning.
- Go to System Settings → Privacy & Security, scroll to Security, and click Open Anyway.