Practice & Challenges — Useful Sites

CP-Algorithms

2026-10-18T00:00:00Z

An English translation and extension of the e-maxx.ru write-ups on competitive-programming algorithms, each topic with code and practice problems. Unlike problem-solving platforms it explains the algorithm itself in depth rather than serving problems.

https://cp-algorithms.com/

SELinux Game

2026-10-18T00:00:00Z

A scenario-based game for learning SELinux that you run on your own machine. It turns the usually dry topic of policy writing into practical debugging tasks. Unlike plain documentation, it teaches policy through debugging tasks.

https://selinuxgame.org/index.html

Python Challenge

2026-10-09T09:00:00Z

A riddle game where each level is solved with a bit of Python. Unlike exercise sites every puzzle hides the next level’s address — you cannot move on without solving it.

https://www.pythonchallenge.com/

Python Koans

2026-10-09T09:00:00Z

A repository that teaches Python by making failing tests (“koans”) pass one at a time. Unlike reading a tutorial you fix real tests, so feedback is immediate.

https://github.com/gregmalcolm/python_koans

Pytudes

2026-10-09T09:00:00Z

Peter Norvig’s short Python programs and notebooks on puzzles, algorithms and language. Unlike exercise sites each is an expert’s worked solution with the reasoning explained.

https://github.com/norvig/pytudes

Snakify

2026-10-09T09:00:00Z

A Python 3 course with 100+ exercises, coded in the browser. Unlike video courses a checker verifies your solution at once.

https://snakify.org/en/

Awesome Code Review

2026-09-18T00:00:00Z

A resource list for the practice of code review. Unlike tool lists, it collects not only review tools but also articles and guidelines on review culture.

https://github.com/joho/awesome-code-review

Beecrowd

2026-09-18T00:00:00Z

An online judge grading programming, mathematics and SQL problems automatically, formerly URI Online Judge. Unlike LeetCode it is learning- rather than interview-oriented, with plenty of beginner problems.

https://www.beecrowd.com.br/judge/en/

Code Golf (Stack Exchange)

2026-09-18T00:00:00Z

A community contest to solve a problem in the shortest possible code. Unlike algorithm sites the measure is code length rather than speed or correctness — it shows how far languages can be bent.

https://codegolf.stackexchange.com/

CodePen Challenges

2026-09-18T00:00:00Z

Front-end (HTML/CSS/JS) challenges with an embedded editor, each round on a new theme. Unlike algorithm sites the result is visual: there is no single right answer, just creative solutions.

https://codepen.io/challenges

Daily Coding Problem

2026-09-18T00:00:00Z

A service that emails one coding-interview problem every day. Unlike problem platforms it lands in your inbox — the point is building a habit; detailed solutions are paid.

https://www.dailycodingproblem.com/

devChallenges.io

2026-09-18T00:00:00Z

A challenge site that has you build web projects with realistic designs and requirements. Unlike random projects the community reviews the solutions.

https://devchallenges.io/

GeeksforGeeks

2026-09-18T00:00:00Z

A very broad article archive of algorithms, data structures and interview questions. Unlike single-topic sites it has a worked example for almost every CS topic.

https://www.geeksforgeeks.org

RealWorld

2026-09-18T00:00:00Z

A spec whose same realistic app (Conduit) is built across different front-end and back-end stacks.

https://realworld.how

Rosetta Code

2026-09-18T00:00:00Z

A wiki showing the same small problem solved in hundreds of languages. Unlike single-language examples it shows side by side how a task differs across languages.

https://rosettacode.org/

TodoMVC

2026-09-18T00:00:00Z

Shows the same to-do app built in dozens of JavaScript frameworks. Unlike the frameworks’ own demos the functionality is held constant, so only the approach changes and you can compare them side by side.

https://todomvc.com

TopCoder Arena

2026-09-18T00:00:00Z

The classic arena for timed algorithm competitions (SRM). Unlike Codeforces it uses the SRM format: after the coding phase comes a challenge phase where you score by feeding failing inputs to other people’s code.

https://arena.topcoder.com/

UVa Online Judge

2026-09-18T00:00:00Z

A classic online judge auto-grading hundreds of contest problems. Unlike newer platforms, it is the archive the problem lists of the Competitive Programming (Halim) book are built on.

https://onlinejudge.org/

Python Tutor

2026-08-19T23:33:57Z

Steps through code drawing stack frames and heap objects. Unlike a classic debugger it visualises memory — nothing explains reference semantics, scope and mutable default arguments as clearly.

https://pythontutor.com/

AlgoDS

2026-08-17T20:53:20Z

Java implementations of algorithms and data structures. Unlike textbook pseudocode, each is real, readable, working code with its tests.

https://github.com/sherxon/AlgoDS

Algorithm Design Canvas

2026-08-17T20:53:20Z

A stepwise framework for approaching an interview algorithm problem — constraints, examples, brute force, optimise, test. Method instead of panic.

https://www.hiredintech.com/algorithm-design

AtCoder

2026-08-17T20:53:20Z

A Japan-based contest platform whose beginner rounds (ABC) are more approachable for newcomers than Codeforces.

https://atcoder.jp/

Big-O Cheat Sheet

2026-08-17T20:53:20Z

A single colour-coded table of time and space complexity for data structures and sorting algorithms. Unlike a textbook it shows everything at a glance — the last look before an interview.

https://bigocheatsheet.com/#

Big-O Yanılgıları

2026-08-17T20:53:20Z

A piece correcting common misunderstandings of big-O notation. Unlike standard explanations, it targets subtle errors directly, such as conflating worst case with average case.

https://ssp.impulsetrain.com/big-o.html

Bit İşlemleri Numaraları

2026-08-17T20:53:20Z

A collection of common bit-level tricks — the patterns that turn up in low-level optimisation and interview questions.

https://gist.github.com/dideler/2365607

CodeAbbey

2026-08-17T20:53:20Z

A problem sequence starting at the very easiest and climbing gradually — a far gentler curve than the contest platforms for absolute beginners.

https://www.codeabbey.com

CodeChef

2026-08-17T20:53:20Z

A competitive algorithm platform with regular contests, difficulty-tagged problems and published editorial solutions. Unlike Codeforces, it offers learning paths and practice sections aimed at beginners.

https://www.codechef.com

Codeforces

2026-08-17T20:53:20Z

The busiest competitive programming platform, with regular rounds and a rating system. Problems run harder than LeetCode and lean heavily mathematical.

https://codeforces.com

CodeGym

2026-08-17T20:53:20Z

A practice-heavy course teaching Java through 1,200 hands-on tasks, with every solution checked automatically. Unlike video courses, it is tasks rather than theory: you advance by writing code.

https://codegym.cc/

Coderbyte

2026-08-17T20:53:20Z

An interview problem bank and assessment tool. Unlike LeetCode it offers video explanations of solutions and also hosts the assessment tool companies use to screen candidates.

https://coderbyte.com/

CodeSignal

2026-08-17T20:53:20Z

A skills assessment and interview platform that produces a standardised score you can send to several companies. The single assessment is the difference from sitting a separate test for every employer.

https://app.codesignal.com

Codility

2026-08-17T20:53:20Z

The assessment platform companies use for technical screening, with a practice section open to candidates. Its difference from other problem sites is that it mirrors the format of real screening tests — you see the exam environment before the exam.

https://app.codility.com/programmers/

CodinGame

2026-08-17T20:53:20Z

A platform that has you solve programming puzzles with a game theme, showing your code’s result in a game scene. Unlike dry problem sets it animates your solution visually.

https://www.codingame.com/

Competitive Programmer’s Handbook

2026-08-17T20:53:20Z

A free handbook for competitive programming, from basic algorithms to advanced techniques. Against academic algorithm books it is contest-oriented: it hands you an implementable template rather than a proof.

https://cses.fi/book.html

CryptoHack

2026-08-17T20:53:20Z

Teaches cryptography by breaking it, with each level exploiting a real weakness. Unlike a theory course it teaches from the attacker’s side — the applied counterpart.

https://cryptohack.org/

freeCodeCamp

2026-08-17T20:53:20Z

A complete free curriculum with in-browser exercises and free certificates. Its capstone projects make you build real applications rather than stopping at drills.

https://www.freecodecamp.com

Google Interview Warmup

2026-08-17T20:53:20Z

A practice tool where you answer interview questions aloud and get AI feedback. Unlike coding-interview sites, it focuses on behavioural and role questions, highlighting the key terms in your answer.

https://grow.google/certificates/interview-warmup/

HackerEarth

2026-08-17T20:53:20Z

Combines contests with hiring assessments — companies run technical screening here. Unlike HackerRank, it is strong on hosting hackathons.

https://www.hackerearth.com

HiredInTech

2026-08-17T20:53:20Z

Structured courses for system-design and algorithm interviews. Unlike problem banks it teaches method rather than questions — a framework for working a problem step by step; the content is old but the framework holds.

https://www.hiredintech.com/

InterviewBit

2026-08-17T20:53:20Z

Gamified interview preparation. Unlike LeetCode’s open problem pool, topics are ordered by dependency, each building on the last.

https://www.interviewbit.com