The arena for programming + AI skills.

[Code, Compete, Create]

Meet with the team

Exit BattleLIVE BATTLE

Battle Lobby

Finding you a worthy opponent...

Searching for opponent

Looking for someone near your skill level.

Problem difficulty is set from your ELO and your opponent's when a match is found. No extra setup needed.

Elapsed

0:00

ELO Band

625-675

Est. time remaining 00:20

Scanning for opponents in your skill range...

Practice this problem

Product evidence

Rooted in real practice, classroom, and assessment work.

The strongest proof today is the product itself: a problem bank, live battle surface, classroom flow, assessment workspace, and the team roots behind them.

10,000+

Problems

curated CS practice items across the arena

Languages

from Python and JavaScript to C++, Rust, and Go

Live

Practice loops

ranked battles, classroom sessions, and replayable work

AI-era

Skill signal

built around planning, verification, and tool fluency

Product lanes

More ways to build real skill.

Guided practice supports the core Compete loop. Classroom is concrete today. Assessments is in progress. AFK and Vibecoding Courses are labeled as early concepts, with enough shape to show where the product family is going.

Guided practice

Practice with hints when you do not want a duel.

Rena can coach the two-sum pattern, edge cases, and testing discipline while the live battle IDE stays the first impression.

Practice this problem

Back to Practice

Problem List

15:35

Time Remaining

Hide Timer

Code

1# Read input from stdin
2# Example: n = int(input())
3# Example: arr = list(map(int, input().split()))

Ln 1, Col 24Spaces: 4

Test Result0/3 Passed (0%)

Testcase

Input

1
11
80011223388

Your Output

Pending...

Expected

YES

All 3 public test cases shown

Classroom

Live CS teaching without the chaos.

Host algorithm quizzes, watch students answer in real time, and debrief the exact concepts that need attention.

Explore Classroom

1197sQ4/5 1 Player

Exit BattleClassroom Code

Code

1# Pair Sum Exists
2import sys
3 
4lines = sys.stdin.read().split("\n")
5nums = list(map(int, lines[0].split()))
6target = int(lines[1])
7 
8seen = set()
9for x in nums:
10    if target - x in seen:
11        print("true")
12        break
13    seen.add(x)
14else:
15    print("false")

Ln 4, Col 37Spaces: 4

Test Result0/15 Passed (0%)

Testcase

Input

2 7 11 15
9

Your Output

Pending...

Expected

true

Custom testsLocal only Saved in the preview, not executed by the demo judge.

Use Add to open editable input fields for edge cases before a full submit.

Classroom coding

Q4/5

First Unique Number

Passed all

Submitted

0/0

Avg tests

Teacher controls

Hints only

No full code

Coding questions

Assessments

In progress

Hiring signal for AI-era engineering.

In-progress recruiter workflows for measuring how candidates plan, prompt, verify, and ship with AI in the loop.

Preview Assessments

Recruiter reportlooping preview

Recommendation

Advance

86%

Strong verifier. Highlight: ai tool usage.

Reviewer summary

The score explains the path: prompt quality, edit ownership, tests, and final correctness.

AI tool usage

Rena + Claude

balanced model choice

Prompt quality

high clarity

constraints + examples

Test discipline

6 runs

verified after edits

Iteration pace

3 cycles

42 min total

AFK

Concept

Away From Keyboard building for owned projects.

Early concept for turning ideas into repos, exports, benchmarks, and real code you can take anywhere.

Preview AFK

AFK conceptearly access

Rena AFK

chat to app workspace

You

Build a tiny web app where students track daily algorithm practice and see streaks.

Generating first pass

Scaffold Next.js dashboard

Add local progress storage

Generate streak card and goal list

Run smoke check

arena-practice-app4 files

app/page.tsx+84

app/api/progress/route.ts+31

components/GoalCard.tsx+42

lib/storage.ts+18

npm run check

lint passed

preview ready

app/page.tsx

1export default function PracticeTracker() {

2 const goals = ["arrays", "graphs", "dp"];

4 return <main className="grid gap-4">

5 <StreakCard days={12} />

6 <GoalList goals={goals} />

7 <RunSummary accepted={8} />

8 </main>;

Browser previewlive

Practice Tracker

June sprint

12 day streak

accepted

topics

42m

focus

Arrays5/6

Graphs2/4

Dynamic programming1/3

Next suggested build: add reminders and weekly review.

Vibecoding Courses

Concept

Learn to code with words, not syntax.

A future course where learners prompt Rena in plain English, watch the assistant translate intent into steps, and discover real CS concepts.

Preview Vibecoding Courses Course waitlist

Vibecoding Courses001 to 050

Task 001live UI

pick

move

drop

first green ball, then nearest green box

Sequencing

Move the right objects in the right order.

Task 002live UI

only move the matching color

Precision

Say exactly what should happen next.

Task 003live UI

filter green

nearest box

repeat

repeat until no green objects remain

Optimization

Find the shortest repeatable plan.

Ask Rena

plain English to CS concepts

Learner

Move every green thing into the nearest matching box.

Rena

Great. That command has a loop, a condition, and a nearest-match rule hiding inside it.

Find green objects

Choose nearest box

Repeat until done

Verify every match

for each object -> if green -> nearest box -> move -> check

Stay close to the frontier.

Non-product surfaces for the ideas, docs, and evidence behind how AlgoArena is being built.

Research and field notes

CS education, AI-era assessments, keystroke/process-signal ideas, and product notes from building in public.

Read field notes

Product notesMay to Jun

CS classroom study

How live coding challenges change practice, debrief, and participation.

Keystroke signals

Process traces for integrity, effort, and AI-era assessment evidence.

LLM build notes

What the prompting, review, and shipping process taught the team.

Platform documentation

A calmer reference surface for product lanes, classroom setup, assessment flows, and how the platform fits together.

Open docs

Docs index

Compete

Classroom

Assessments

Vibecoding Courses

Classroom setup

Host a live algorithm session

Create quiz

Share room code

Review debrief

Benchmarks and evidence

The public direction for scoring, judging quality, and evidence that explains more than a pass/fail result.

Explore benchmarks

Evidence modelscoring notes

Tests

3/3

Process

clear

AI use

reviewed

Reviewer summary

Score should explain the path: prompt quality, edit ownership, test discipline, and final correctness.

Replay attached

Rubric notes

Product updates

Stay in the loop

Get updates as Assessments, AFK, and Vibecoding Courses move from concept to real product.

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Live updates on battles & training

FAQ

Explore Classroom Preview Assessments Preview AFK Preview Vibecoding Courses

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Ask another model

Not sure if AlgoArena is right for you?

Open a prefilled prompt in the AI tool you already use and pressure-test the fit from the outside.

Ask ChatGPT

Ask Claude

Ask Gemini

Ready to jump in?

Start with the concrete practice loop today, or explore the product lanes shaping where AlgoArena goes next.