Projects in Awesome Lists tagged with algorithm-challenges

My Solutions to Leetcode problems. All solutions support C++ language, some support Java and Python. Multiple solutions will be given by most problems. Enjoy:) 我的Leetcode解答。所有的问题都支持C++语言，一部分问题支持Java语言。近乎所有问题都会提供多个算法解决。大家加油！：）

algorithm-challenges algorithm-competitions algorithms interview-questions leetcode-cpp leetcode-solutions

Last synced: 15 May 2025

https://github.com/liuyubobobo/Play-Leetcode

My Solutions to Leetcode problems. All solutions support C++ language, some support Java and Python. Multiple solutions will be given by most problems. Enjoy:) 我的Leetcode解答。所有的问题都支持C++语言，一部分问题支持Java语言。近乎所有问题都会提供多个算法解决。大家加油！：）

algorithm-challenges algorithm-competitions algorithms interview-questions leetcode-cpp leetcode-solutions

Last synced: 25 Mar 2025

https://github.com/java-aid/hackerrank-solutions

30-days-of-code algorithm-challenges algorithms-and-data-structures coding-challenges cracking-the-coding-interview data-structures-and-algorithms hackerrank-algorithms-solutions hackerrank-algorithms-youtube hackerrank-all-solutions hackerrank-challenges hackerrank-ctci hackerrank-implementation hackerrank-java hackerrank-practice hackerrank-problem-solutions hackerrank-problem-solving hackerrank-solutions hackerrank-solutions-for-java hackerrank-solutions-github

Last synced: 15 May 2025

https://github.com/Java-aid/Hackerrank-Solutions

30-days-of-code algorithm-challenges algorithms-and-data-structures coding-challenges cracking-the-coding-interview data-structures-and-algorithms hackerrank-algorithms-solutions hackerrank-algorithms-youtube hackerrank-all-solutions hackerrank-challenges hackerrank-ctci hackerrank-implementation hackerrank-java hackerrank-practice hackerrank-problem-solutions hackerrank-problem-solving hackerrank-solutions hackerrank-solutions-for-java hackerrank-solutions-github

Last synced: 03 Apr 2025

https://github.com/tech-cow/leetcode

👏🏻 leetcode solutions for Humans™

algiorithimcs algorithm algorithm-challenges algorithm-competitions algorithms algorithms-and-data-structures algorithms-datastructures google interview interview-practice interview-preparation interview-questions interview-test leetcode leetcode-python leetcode-solutions python python-leetcode

Last synced: 16 May 2025

https://github.com/iiitv/algos

Popular Algorithms and Data Structures implemented in popular languages

algorithm algorithm-challenges algorithms code-list codes data-structures hacktoberfest

Last synced: 15 May 2025

https://github.com/sahilbansal17/get_better_at_cp_in_2_months

This contains the curriculum that I will follow to get better at Competitive Programming in 2 months.

algorithm algorithm-challenges algorithm-competitions algorithm-library algorithms algorithms-and-data-structures algorithms-datastructures algorithms-implemented competitive-coding competitive-programming competitive-programming-algorithms competitive-programming-contests competitive-programming-reference competitive-sites competitiveprogramming data-structures

Last synced: 24 Mar 2025

https://github.com/sahilbansal17/Get_Better_at_CP_in_2_Months

This contains the curriculum that I will follow to get better at Competitive Programming in 2 months.

algorithm algorithm-challenges algorithm-competitions algorithm-library algorithms algorithms-and-data-structures algorithms-datastructures algorithms-implemented competitive-coding competitive-programming competitive-programming-algorithms competitive-programming-contests competitive-programming-reference competitive-sites competitiveprogramming data-structures

Last synced: 14 May 2025

https://github.com/sudheerj/datastructures-algorithms

List of Programs related to data structures and algorithms

algorithm-challenges algorithms datastructures datastructures-algorithms dsa dsa-algorithm dynamic-programming graph interview java javascript leetcode linkedlist lodash polyfills prototype queue stack tree

Last synced: 15 May 2025

https://github.com/omonimus1/geeks-for-geeks-solutions

✅ My own Amazon, Microsoft and Google SDE Coding challenge Solutions (offered by GeeksForGeeks).

algorithm-challenges algorithms-and-data-structures amazon amazon-coding-challenge bst competitive-programming competitive-programming-algorithms geeks geeks-solutions geeksforgeeks geeksforgeeks-cpp geeksforgeeks-interview-prep geeksforgeeks-solutions graph linked-list matrix microsoft-practices stack tree vector

Last synced: 07 Apr 2025

https://github.com/jiayangwu/leetcode-python

LeetCode solutions in Python2. LeetCode题解 in Python2。

algorithm-challenges algorithms chinese interview-practice interview-preparation interview-questions interview-questions-solved leetcode leetcode-practice leetcode-python leetcode-solutions python2

Last synced: 04 Apr 2025

https://github.com/sahilbansal17/competitive_coding

This repository contains some useful codes, techniques, algorithms and problem solutions helpful in Competitive Coding.

algorithm algorithm-analysis algorithm-challenges algorithm-competitions algorithm-library algorithms algorithms-and-data-structures algorithms-implemented competitive-coding competitive-programming competitive-programming-algorithms competitive-programming-contests competitive-programming-reference cpp data-structures graph graph-algorithms hacktoberfest hacktoberfest2019 programming-contests

Last synced: 05 Apr 2025

https://github.com/mebeim/aoc

🎄 My solutions and walkthroughs for Advent of Code and more related stuff.

advent-of-code algorithm-challenges competitive-programming programming-challenges programming-puzzles python python3

Last synced: 16 May 2025

https://github.com/StBogdan/CTCI_python

Solutions for Interview questions appearing in the 6th edition of Cracking the Coding Interview (CTCI)

algorithm-challenges algorithms-and-data-structures ctci-6th ctci-python ctci-solutions ctci6

Last synced: 01 Apr 2025

https://github.com/dipeshpatil/algorithms-visualiser

A tool made using ReactJS to visualise algorithms!

algorithm-challenges algorithms bfs javascript nodejs open-source opensource react reactjs visualisers

Last synced: 19 Mar 2025

https://github.com/Vishruth-S/CompetitiveCode

A repo for interesting Competitive Coding problems

algorithm-challenges competitive-coding competitive-programming programming

Last synced: 20 Apr 2025

https://github.com/jonasraoni/codility

My solutions to exercises and tests at http://codility.com.

algorithm-challenges algorithms algorithms-and-data-structures algorithms-csharp codility codility-100 codility-challenges codility-csharp codility-exercises codility-lessons codility-lessons-exercises codility-solutions codility-training competitive-programming csharp

Last synced: 12 Apr 2025

https://github.com/WoMakersCode/challenges-algorithms

Repositório referente à desafios sobre algoritmos da womakerscode

algorithm-challenges algorithms challenge hacktoberfest java javascript

Last synced: 12 Apr 2025

https://github.com/batermj/data_sciences_campaign

【数据科学家系列课程】

algorithm-analysis algorithm-challenges algorithm-visualisation algorithms architectural-patterns architecture-visualization architectures artificial-intelligence automatic-machine-learning automation data-science design-patterns foundation-framework machine-learning-algorithms mathematical-statistics mathematics product-design robotics startup system-architecture

Last synced: 05 Apr 2025

https://github.com/gabrieldim/algorithms-and-data-structures

Algorithms and data structures tasks - examples.

algorithm algorithm-challenges algorithms algorithms-and-data-structures

Last synced: 27 Oct 2025

https://github.com/dbz/algorithms

Data Structures & Algorithms. Includes solutions for Cracking the Coding Interview 6th Edition

algorithm algorithm-challenges algorithms computer-science cracking-the-coding-interview data-structures datastructures graph heap javascript python queue ruby stack stacks sum tree trees trie tries

Last synced: 16 Apr 2025

https://github.com/boudhayan/algorithm-solutions-in-swift

This repository contains 250+ data structures and algorithms solutions from AlgoExpert, LeetCode & HackerRank in Swift 🧑🏻‍💻

algoexpert algoexperts algorithm algorithm-challenges algorithms algorithms-and-data-structures algorithms-implemented hackerrank hackerrank-solutions interview-preparation interview-questions leetcode leetcode-practice leetcode-questions leetcode-solutions leetcode-swift

Last synced: 28 Oct 2025

https://github.com/onecodemonkey/algorithm

📝 Daily accumulate of algorithm. Leetcode Solutions | Codeforces Solutions

algorithm algorithm-challenges algorithms codeforces codeforces-problems codeforces-solutions codeforces-solutions-github data-structures datastructures leetcode leetcode-java leetcode-questions leetcode-solutions

Last synced: 05 Apr 2025

https://github.com/nirgn975/challenges

My solutions for random coding challenges 💪

algorithm algorithm-challenges challenges code-challenge codewars crackmes data-structrues hackerrank javascript python

Last synced: 20 Mar 2025

https://github.com/anfany/codility-lessons-by-python3

为编程、算法、Python3的初学者，提供基于Codility课程习题的全套解决方案(中文题目+解题思路+Python3代码)

algorithm algorithm-challenges code codility codility-lessons python3

Last synced: 09 Apr 2025

https://github.com/dtcxzyw/oi-source

OI代码仓库、复习笔记、代码模板、本地Judger

acm-icpc acm-icpc-handbook algorithm algorithm-challenges automated-testing competitive-programming data-structures icpc icpc-training judger noi noip oi oi-handbook oi-training olympiad-in-informatics

Last synced: 23 Mar 2025

https://github.com/omonimus1/hackerrank-solutions

My own HackerRank coding interview solutions

algorithm-challenges algorithms-and-data-structures coding-challenge cpp hackerrank hackerrank-challenges hackerrank-cpp hackerrank-python hackerrank-solutions hackerrank-sql-solutions interview-preparation interview-preparation-kit java javascript mysql python sql

Last synced: 17 Mar 2025

https://github.com/espressopp/espressopp

Main ESPResSo++ repository

adress algorithm-challenges algorithmic analysis c-plus-plus devtools espresso hpc-applications lattice-boltzmann method python

Last synced: 18 Dec 2025

https://github.com/msdundar/notes-algorithms

A brief summary of various algorithms. Each algorithm provides examples written in Python, Ruby and GoLang.

algorithm-challenges algorithms algorithms-and-data-structures bcrypt bellman-ford-algorithm big-o-notation binary-search breadth-first-search dijkstra-algorithm divide-and-conquer greedy-algorithms grokking-algorithms hash-tables k-nearest-neighbours quicksort recursion selection-sort

Last synced: 19 Apr 2025

https://github.com/justehmadsaeed/timetable-scheduler

⏲ An Activity Scheduling Project of Algorithms Analysis to schedule the timetable for Educational Institutes.

algorithm-challenges algorithms algorithms-and-data-structures algorithms-implemented hacktoberfest time-schedule timetable-generator

Last synced: 14 Sep 2025

https://github.com/houarizegai/problem-solving

Problems with my solutions of Daily Coding Problem website

algorithm-challenges daily-coding-problem

Last synced: 10 Apr 2025

https://github.com/bepb/hackerrank_sql

cracking-the-coding-interview algorithm-challenges coding-challenges hackerrank-sql

algorithm-challenges algorithms-and-data-structures-30-days-of-code coding-challenges cracking-the-coding-interview data-structures-and-algorithms hackerrank-algorithms-solutions hackerrank-all-solutions hackerrank-challenges hackerrank-practice hackerrank-problem-solutions hackerrank-problem-solving hackerrank-solutions hackerrank-solutions-for-sql hackerrank-solutions-github hackerrank-sql

Last synced: 01 Nov 2025

https://github.com/josancamon19/algoexpert-python

AlgoExpert data structures and algorithms exercises in python.

algoexpert algorithm-challenges algorithms-and-data-structures

Last synced: 12 Apr 2025

https://github.com/ashtanko/dsa-kotlin

📚 Collection of various Data Structures and Algorithms, implemented in Kotlin for educational purposes.

algorithm-challenges algorithms algorithms-and-data-structures algorithms-datastructures computer-science datastructures detekt interview interview-practice kotlin learn-to-code sort sorting-algorithms

Last synced: 12 Apr 2025

https://github.com/ferhatelmas/algo

:books: My solutions to algorithm problems on various websites

algorithm algorithm-challenges

Last synced: 17 Mar 2025

https://github.com/rohan-paul/Algorithm-in-JavaScript

Implementing all-time classic algorithmic problems in JS

algorithm-analysis algorithm-challenges algorithms algorithms-and-data-structures algorithms-implemented algorithms-python javascript python python-3 python3

Last synced: 17 Apr 2025

https://github.com/tar3q-az1z/codeforces-solutions

Contains solutions of algorithmic problems from codeforces solved by me.

algorithm-challenges algorithms codeforces coding-challenges competitive-programming cplusplus git github java python repository software-development solutions

Last synced: 13 Apr 2025

https://github.com/papachristoumarios/ieeextreme11.0

:rocket: IEEEXtreme 11.0 Solutions by PComplete Team (48th Rank Worldwide)

algorithm-challenges algorithms competition competitive-programming ieeextreme

Last synced: 07 Aug 2025

https://github.com/kamyu104/facebookhackercup-2020

🏃 Python Solutions of All 24 Problems in FHC 2020

algorithm algorithm-challenges competitive-programming contest-programming facebook-hacker-cup hackercup programming-contests puzzle-solution

Last synced: 01 Jul 2025

https://github.com/omarelgabry/cubes

Implementation of interesting algorithms in C++

algorithm-challenges algorithms c-plus-plus competitive-programming

Last synced: 05 Oct 2025

https://github.com/posquit0/hackerrank

my solutions for hackerrank.com

algorithm algorithm-challenges c-plus-plus hackerrank

Last synced: 15 Apr 2025

https://github.com/kamyu104/metahackercup-2022

🏃 Python3 Solutions of All 30 Problems in MHC 2022

algorithm algorithm-challenges competitive-programming contest-programming facebook-hacker-cup hackercup meta-hacker-cup programming-contests puzzle-solution

Last synced: 01 Jul 2025

https://github.com/ashtanko/kotlin-lab

📚 Algorithms, Data Structures, Design Patterns, Concurrency in Kotlin

algorithm-analysis algorithm-challenges algorithms algorithms-and-data-structures computer-science concurrency coroutines data-structures kotlin leetcode queue sorting-algorithms stack trie

Last synced: 12 Apr 2025

https://github.com/HEX9CF/NekoACM

🐱🐾NekoACM: Neural-network Engine Kit of ACM-ICPC. 基于人工智能大模型的 ACM-ICPC 神经网络引擎工具包，提供自动出题、生成测试数据和题解代码、题目格式解析、题目国际化翻译、虚拟评测机、AI 编程助手等功能。可以作为模块集成到 Online Judge 系统中。

acm-icpc ai ai-agents ai-assistant aigc algorithm-challenges chatgpt competitive-programming gin go gpt icpc llm oj online-judge openai

Last synced: 05 May 2025

https://github.com/baeharam/ps

하루에 1개 이상의 PS를 하기위한 저장소 :memo:

algorithm-challenges problem-solving

Last synced: 14 Apr 2025

https://github.com/kamyu104/facebookhackercup-2019

🏃 Python Solutions of All 22 Problems in FHC 2019

algorithm algorithm-challenges competitive-programming contest-programming facebook-hacker-cup hackercup programming-contests puzzle-solution

Last synced: 01 Jul 2025

https://github.com/autumnchris/freecodecamp-algorithms

My solutions to the JavaScript Algorithms on freeCodeCamp.

algorithm-challenges algorithm-scripting algorithms freecodecamp freecodecamp-algorithms freecodecamp-certification freecodecamp-curriculum javascript javascript-algorithms

Last synced: 10 Apr 2025

https://github.com/kamyu104/facebookhackercup-2021

🏃 Python Solutions of All 27 Problems in FHC 2021

algorithm algorithm-challenges competitive-programming contest-programming facebook-hacker-cup hackercup programming-contests puzzle-solution

Last synced: 01 Jul 2025

https://github.com/pdeljanov/leetcode

Accepted C++ solutions to LeetCode problems

algorithm-challenges algorithms interview-practice leetcode leetcode-solutions

Last synced: 11 Apr 2025

https://github.com/adebsalert/data-structure-algorithm

Practice repo for solving leetcode problems and also custom data structures

algorithm-challenges algorithms-and-data-structures data-structures leetcode

Last synced: 04 Oct 2025

https://github.com/surewht/js-test

tests for javascript developers

algorithm-challenges algorithms balanced-parentheses caesar-cipher es6 fibonacci-sequence fizzbuzz geometric-algorithms internship javascript job-interviews junior-developer learning learning-by-doing palindrome reduce test-driven-development

Last synced: 13 May 2025

https://github.com/prabaprakash/data-structures-and-algorithms-programs

Algorithm and Data Structures

algorithm-challenges algorithms data-structures dynamic-programming problem-solving

Last synced: 11 Apr 2025

https://github.com/thinktankshark/algorithm_solutions

Algorithm Problems and Solutions in JavaScript

algorithm algorithm-challenges algorithm-solutions hackerrank-solutions javascript leetcode-solutions

Last synced: 23 Mar 2025

https://github.com/pct960/competitive_programming

A handy collection of implemented data structures and algorithms for competitive coding contests

algorithm-challenges algorithms algorithms-implemented competitive-programming data-structures java

Last synced: 19 Oct 2025

https://github.com/ice1000/oi-codes

:closed_lock_with_key: Solutions for online code challenges. Don't be evil.

acm acm-icpc algorithm algorithm-challenges algorithms c cpp crystal dart elixir haskell javascript oi ruby rust solutions typescript

Last synced: 18 Mar 2025

https://github.com/teddyoweh/rest-api-hackerank

My Solution to the Hacker Rest API Intermediate Problems

algorithm-challenges algorithms api hackerrank hackerrank-solutions python rest-api

Last synced: 17 Jul 2025

https://github.com/siddhpant/google-foobar

My approach to Google foobar challenges.

algorithm-challenges computer-science foobar foobar-challenge foobar-solutions google-foobar interview-questions mathematical-programming not-completely-terrible writeups

Last synced: 07 Jul 2025

https://github.com/teddyoweh/teddyoweh

algorithm-challenges algorithms-and-data-structures backend-development competitive-programming flask javascript laravel machine-learning machine-learning-algorithms mysql php python react-native reactjs software-development

Last synced: 01 Jul 2025

https://github.com/dhanushnehru/leetcode

Collection of LeetCode problems solved

algorithm-challenges algorithms-and-data-structures algorithms-interview-questions datastructures datastructures-algorithms dsa leetcode leetcode-javascript leetcode-javascript-solutions leetcode-python leetcode-solution leetcode-solutions leetcode-solutions-javascript problem-solving

Last synced: 12 Aug 2025

https://github.com/arasgungore/learning-c-programming

An archive containing all of the Turkish C coding lectures and exercises I have written back when I have started learning programming.

algorithm-challenges c-programming c-programming-language codeforces-problems codeforces-solutions coding coding-exercises coding-practices coding-problems hackerrank-algorithms-solutions hackerrank-solutions introduction-to-programming learn-coding learn-programming learn-to-code learning-c learning-code learning-notes learning-programming turkish-programming

Last synced: 10 Apr 2025

https://github.com/devfinwiz/leetcode-feeder

A repository designed for novice developers to make open-source contributions with just a few clicks. Get your pull request merged in under 12 hours!

algorithm-challenges competitive-coding cpp data-structures java leetcode leetcode-python python sql

Last synced: 21 Mar 2025

https://github.com/gokgokalp/algorithm-playground

This repository contains my solutions and personal notes about algorithms.

algorithm algorithm-challenges algorithms csharp dotnet

Last synced: 10 Jul 2025

https://github.com/teddyoweh/college-students-clustering

Implementing Kmeans on a College Students database based on their iq and cgpa and using creating linear regression model to predict the clusters students belong to

algorithm-challenges kmeans-clustering kmeans-clustering-algorithm linear-regression machine-learning machine-learning-algorithms

Last synced: 09 Apr 2025

https://github.com/teddyoweh/proving-orthogonal-vectors

A function created to parse two vector and follow an alogrithm to prove if the vectors are Orthogonal ( Perpendicular) or not.

algorithm-challenges algorithms calculus pre-calclus python vectors

Last synced: 09 Apr 2025

https://github.com/simonzhangiter/js-algorithm

DataStructure、Algorithm by JavaScript

algorithm algorithm-challenges algorithms-datastructures datastructures javascript js-algorithms optimization-algorithms

Last synced: 02 Aug 2025

https://github.com/esotericpig/codewars

:space_invader::school_satchel::neckbeard: My codewars solutions: Ruby, Java, Python, C++, JavaScript, Crystal, Kotlin, CoffeeScript, PHP, Objective-C.

algorithm-challenges algorithms codewars codewars-solutions katas

Last synced: 11 Apr 2025

https://github.com/teddyoweh/vector-algorithms

aSolving vectors related problem ( Vector Magnitude, Vector Dot Product, Vector Angle)

algorithm-challenges algorithms dotproduct scalar vector

Last synced: 25 Aug 2025

https://github.com/lucasbotang/leetcode

My solutions for LeetCode

algorithm-challenges algorithms leetcode python sql

Last synced: 12 Apr 2025

https://github.com/icyjoseph/codejam-js

Solutions to Code Jam and Kick Start problems.

algorithm-challenges babel codeforces codejam competitive-programming es6 javascript kickstart rust swift

Last synced: 10 Jul 2025

https://github.com/liuyubobobo/hackerrank-cracking-the-coding-interview

A repo based on the HackerRank Tutorials Course "Cracking the Coding Interview Challenges". All problems are solved by C++.

algorithm algorithm-challenges hackerrank interview-practice

Last synced: 04 Aug 2025

https://github.com/ifpabelem/80questoesjava

80 Questões resolvidas da disciplina Linguagem de Programação e Orientação à Objetos

algorithm-challenges algorithms hacktoberfest ifpa java poo

Last synced: 03 Mar 2025

https://github.com/koeonyack/levelup-algorithm

🔥 500문제 돌파🔥 🚀 알고리즘 실력을 올리기 위한 연습 👨‍💻

algorithm algorithm-challenges algorithmic-trading algorithms-and-data-structures

Last synced: 08 May 2025

https://github.com/kalwar/codility

Codility challenges and solutions

algorithm-challenges algorithms challenges challenging-algorithms codility codility-solutions coding-challenge coding-challenges coding-interview

Last synced: 23 Apr 2025

https://github.com/liuyubobobo/play-advent-of-code

My solutions to Advert of Code (http://adventofcode.com/) . All solutions support C++, some support Java and Python:)

advent-of-code algorithm-challenges

Last synced: 27 Jun 2025

https://github.com/theoludwig/programming-challenges

Programming exercises and challenges to improve your algorithmic logic.

algorithm-challenges challenges gitpod programming-challenges

Last synced: 11 Apr 2025

https://github.com/kutyel/typescript-algorithms

🤓 A small set of algorithms as I learn them

algorithm-challenges algorithms algorithms-implemented interview-questions typescript

Last synced: 15 Apr 2025

https://github.com/basemax/worldalgorithms

Analyzing popular algorithms from the world of algorithms ...

algorithm algorithm-analysis algorithm-challenges algorithms algorithms-and-data-structures algorithms-datastructures algorithms-implemented c

Last synced: 05 May 2025

https://github.com/gouthampradhan/uva-online-judge

UVA online judge solutions

algorithm-challenges algorithms coding-challenge coding-challenges coding-interviews competitive-programming java uva-online-judge uva-solutions

Last synced: 26 Jun 2025

https://github.com/piryanshu88/solve-hackerrank-problems-with-me-javascript-

here you can find Hackerrank Problems solutions, not only code but also I try to give you the approach of solution

algorithm-challenges algorithms-and-data-structures hackerrank hackerrank-30 hackerrank-algorithms-solutions hackerrank-challenges hackerrank-solutions javascript js problem-solving problemsolving

Last synced: 03 Aug 2025

https://github.com/kupolak/codewars

Solved codewars problems.

algorithm-challenges algorithms challenges-solved codewars codewars-challenges codewars-kata codewars-kata-solution codewars-solutions codewars-training-exercise katas programming-challenge programming-challenges programming-exercise programming-exercises programming-katas

Last synced: 25 Mar 2025

https://github.com/alirezaomidi/acm

ACM problems solutions

acm acm-icpc algorithm algorithm-challenges c-plus-plus java programming-challenges programming-contests python

Last synced: 13 Apr 2025

https://github.com/paulsagar1a/data-structure-and-algorithm

For learning and development purpose

algorithm-challenges algorithms algorithms-and-data-structures array datastructures greedy-algorithms heap interview-practice linked-list matrix miscellaneous stack-queue string

Last synced: 04 Apr 2025

https://github.com/cihat-kose/techno-study-java-projects

A collection of Java projects developed as part of the Techno Study program, covering a range of Java concepts from basics to advanced implementations.

algorithm-challenges datastructures java learning-by-doing oops-in-java programming-projects training-materials