Coding interview practice,
with a copilot that explains.
Solve real interview problems in a live in-browser editor. Write in JavaScript or Python, run against actual test cases, and learn the pattern with brute-force → optimal solutions, hints, and AI feedback on your own code.
JavaScript & Python · real test cases · nothing to install
function twoSum(nums, target) {
const seen = {};
for (let i = 0; i < nums.length; i++) {
const need = target - nums[i];
if (need in seen) return [seen[need], i];
seen[nums[i]] = i;
}
}Practice the problems asked at
Not another problem dump
Every problem runs your code for real and teaches you the pattern behind it.
Your code actually runs
Write in JavaScript or Python and run it against real test cases — right in your browser, nothing to install. Pass/fail in seconds, powered by real CPython (WASM) and JS engines.
Solutions that explain
Stuck? Every problem builds up brute-force → optimal, with the reasoning and time/space complexity — so you learn the pattern, not just the answer.
Hints, one at a time
A nudge when you want it — revealed one step at a time, so you can get unstuck without spoiling the whole solution.
AI feedback on your code
Get a review of your actual solution — correctness, edge cases, and how to tighten it — the way a strong interviewer would walk you through it.
The problems that matter
Work the Blind 75 and other curated interview sets — the questions that actually show up, tagged by company, topic, and difficulty.
A real interview workspace
A proper editor with syntax highlighting, a resizable console, and per-test results — the closest thing to the screen you’ll face on the day.
How it works
From cold to confident in three steps.
Pick a problem
Filter the Blind 75 by topic, difficulty, or company and open one in the editor.
Write & run
Solve it in JavaScript or Python and run against live test cases until everything passes.
Learn the pattern
Reveal the optimal solution, take a hint, or get AI feedback — then move to the next.
Questions, answered
Does my code really run?
Yes. JavaScript runs natively in your browser and Python runs on real CPython compiled to WebAssembly — your solution executes against actual test cases and you see exactly which pass and fail. No installs, no setup.
Which languages can I use?
JavaScript and Python today — the two most common coding-interview languages. Every problem ships starter code for both.
What problems are included?
Curated interview problems starting with the Blind 75 — the classic must-do set — tagged by topic, difficulty, and the companies that ask them.
How is this different from grinding problems alone?
You do not just get a right/wrong. You get solutions that build brute-force → optimal with the reasoning, progressive hints, and AI feedback on your own code — so each problem actually teaches you the pattern.
Your next coding round starts here.
Open a problem, write your solution, and watch the test cases turn green. Free to start.
Start practicing free