OpenCodeLeet

This repository was created to test the capabilities of OpenCode and is for learning purposes only.

A local LeetCode-style coding challenge platform supporting Python and Kotlin. Solve algorithm problems in a web editor, run code against test cases on a local server, and get instant feedback.

Quick Start

pip install flask
python3 python/app.py

Open http://127.0.0.1:5000 in your browser.

Tip: Press Ctrl+Enter (or Cmd+Enter on Mac) to run code without clicking the button.

Kotlin (Optional)

To solve challenges in Kotlin, install the Kotlin compiler. Choose your language from the dropdown in the editor toolbar — the server will use kotlinc + java -jar to compile and run.

Deploy to Render (Free)

1. Push this repo to GitHub
2. Go to dashboard.render.com/blueprints
3. Click New Blueprint and connect your repo
4. The included render.yaml and Dockerfile will automatically build and deploy
5. The site is live at https://opencodeleet.onrender.com/

Note: Render's free tier spins down after 15 min of inactivity. First request after idle takes ~30s to wake up.

Features

• Dual language support — switch between Python and Kotlin per challenge, code saved independently per language
• Code editor with syntax highlighting, line numbers, bracket matching (CodeMirror with Dracula theme)
• Server-side execution in an isolated subprocess with a configurable timeout (default 3s)
• Test result parsing — results extracted from stdout markers (ALL_TESTS_PASSED, TEST_FAILED:, ERROR:)
• Solution unlock — after 3 failed attempts on a challenge, a reference solution is revealed
• Execution timing — elapsed time displayed per run in milliseconds
• Auto-save — code persisted to localStorage per challenge per language, survives page reloads
• Error line highlighting — error locations shown in the editor gutter and scrolled into view
• Difficulty-based sidebar — challenges grouped by Easy / Medium / Hard with color-coded badges

Run Tests

python3 python/test_app.py

Adding a Challenge

1. Create a new .py file in challenges/ (e.g., challenges/my-challenge.py)
2. Define a CHALLENGE dict with the keys below
3. Restart the server — the loader picks up new files automatically

Key	Description
id	URL-safe slug (e.g., "my-challenge")
title	Display name (e.g., "1. My Challenge")
difficulty	"Easy", "Medium", or "Hard"
description	HTML string describing the problem
starter_code	Dict keyed by language — initial code the user sees
solution_code	Dict keyed by language — reference solution (unlocked after 3 fails)
test_code	Dict keyed by language — assertion harness that prints stdout markers

Each language entry must contain complete, runnable code that prints one of these markers:

• ALL_TESTS_PASSED
• TEST_FAILED: <message>
• ERROR: <message>

Challenges (60 Total)

Easy (24)

#	Challenge	Solution
1	Two Sum	Hash Map
2	Reverse String	Two Pointers
3	Palindrome Number	Math
4	Valid Parentheses	Stack
5	Contains Duplicate	Hash Set
6	Maximum Subarray	Kadane's Algorithm
7	Move Zeroes	Two Pointers
8	Best Time to Buy and Sell Stock	Greedy
9	Climbing Stairs	Fibonacci DP
10	Single Number	XOR
11	Missing Number	XOR / Math
12	First Unique Character in a String	Hash Map
13	Roman to Integer	Hash Map
14	Longest Common Prefix	Horizontal Scan
15	Plus One	Math
16	Power of Three	Math
17	Fizz Buzz	Simulation
18	Add Binary	Math
19	Pascals Triangle	DP
20	Remove Duplicates from Sorted Array	Two Pointers
21	Sqrt(x)	Binary Search
22	Happy Number	Hash Set / Cycle Detection
23	Intersection of Two Arrays	Hash Set
24	Majority Element	Boyer-Moore Voting

Medium (24)

#	Challenge	Solution
1	Longest Substring Without Repeating Characters	Sliding Window
2	Three Sum	Two Pointers
3	Group Anagrams	Hash Map
4	Longest Palindromic Substring	Expand Around Center
5	Container With Most Water	Two Pointers
6	Product of Array Except Self	Prefix/Suffix
7	Coin Change	DP
8	Longest Increasing Subsequence	Patience Sorting
9	Set Matrix Zeroes	In-Place Markers
10	Rotate Image	Transpose + Reverse
11	Spiral Matrix	Boundary Traversal
12	Jump Game	Greedy
13	Unique Paths	DP
14	Word Search	DFS / Backtracking
15	Top K Frequent Elements	Hash Map + Heap
16	Sort Colors	Dutch Flag
17	Find the Duplicate Number	Floyd's Cycle
18	House Robber	DP
19	Binary Tree Level Order Traversal	BFS
20	Number of Islands	DFS
21	Subarray Sum Equals K	Prefix Sum + Hash Map
22	Find All Anagrams in a String	Sliding Window
23	Decode Ways	DP

Hard (12)

#	Challenge	Solution
1	Trapping Rain Water	Two Pointers
2	First Missing Positive	Cycle Sort
3	Median of Two Sorted Arrays	Binary Search
4	Sliding Window Maximum	Deque
5	Merge k Sorted Lists	Min-Heap
6	Largest Rectangle in Histogram	Stack
7	Longest Valid Parentheses	Stack / DP
8	Edit Distance	DP
9	Minimum Window Substring	Sliding Window
10	Maximal Rectangle	Stack
11	Candy	Two-Pass Greedy
12	Word Ladder	BFS

Project Structure

Dockerfile            Container image (Python 3.11 + JDK 17 + Kotlin 2.1)
render.yaml           Render Blueprint config for one-click deploy
requirements.txt      Python dependencies (Flask)
challenges/           60 .py files — one per challenge (auto-imported)
python/
├── app.py              Flask routes and server entrypoint
├── loader.py           Auto-imports challenge files, strips title numbers
├── config.py           App constants (timeout, host, port, version)
├── runner.py           Subprocess execution engine (Python + Kotlin)
├── test_app.py         Unit tests (16 tests)
└── templates/
    └── index.html      Single-page frontend (Tailwind, CodeMirror, language switcher)

Tech Stack

Layer	Technology
Backend	Python, Flask
Frontend	Tailwind CSS, CodeMirror 5, FontAwesome
Languages	Python (built-in), Kotlin (requires kotlinc)
Testing	unittest
Execution	Subprocess with 3s timeout
Solution Reveal	After 3 failed attempts per challenge per language

License

This project is for educational purposes. Challenge problems are sourced from LeetCode.