For developers
Build the ability. Show the work.
Practice coding, SQL, and working with AI on real tasks. Every answer runs against tests, so you see what works, what breaks, and what to fix next.
- coding problems
- 1,000+
- languages
- 22
- SQL engines
- 6
- practice modes
- 7
def two_sum(nums, target):
for i in range(len(nums)):
for j in range(i + 1, len(nums)):
if nums[i] + nums[j] == target:
return [i, j]Examples
[2,7,11,15], 9Passed[3,2,4], 6Passed[3,3], 6Passed
Hidden tests
Hint: the large cases need a single pass. What could you remember as you go?
Seven ways to practice.
Build and solve on your own, or review and verify work the way teams now ship with AI.
Build and solve
Review and verify
- AI code reviewRead what an AI wrote, flag what is wrong, and fix only what must change.
- Test writingWrite tests that pass every correct version and catch every buggy one.
- PR reviewReview a teammate's pull request, rank what you find, and make the merge call.
- AI agent oversightDecide how much an AI agent may do on its own, round by round.
How a practice round works.
Practice builds transferable skills. Employer assessments are configured separately around each company's work and do not expose private question lists.
Pick a task
Filter by mode, topic, and difficulty. Each task says what it asks of you.
Run the examples
Try your code on the shown examples and on your own inputs before you submit.
Submit against hidden tests
Hidden cases probe the edges. You see what kind of failure happened, never the hidden answers.
Learn from the result
Take a hint and try again, or read the editorial once you solve it. Progress saves to your account.
Free practice
Start with one task.
Pick a task, try an approach, and use the feedback to improve. Your progress saves to your account.