Kotlin coding challenges

This repository contains a set of programming challenges that are intended to be solved by using the Kotlin language (hints, solutions tests and useful links are here as well).

The purpose of this repository is to help you to practice coding and develop strong problem-solving skills. This will help you to become a better programmer and improve your chance of getting a new job by passing whiteboard coding interviews.

Challenge structure

Each challenge is located in a separate package, and it contains 3 main files (screen):

README.md - the task description.
Challenge.kt - file containing an empty method/class where the challenge should be solved. This file also contains a set of tests and occasionally helper methods. You can run all tests directly from this file (click the green arrow next to Test class). JUnit tests which verify that the task was solved correctly.
Solution.kt - a file containing one or more solutions.

Keep in mind that each challenge will usually have more than one solution. Even simple challenges like String reversal can be solved in 10 different ways. Usually, we compare various solutions using (Big O notation) to determine space/time complexity, and we look at code readability.

How do I start?

Install IntelliJ IDEA
Import the project by using the IntelliJ IDEA menu: File | New | Project From Version Control | Git
Choose a challenge (src\test\kotlin\com\igorwojda package) and code the solution in the Challenge.kt file
Run the tests in the Challenge.kt file to verify the provided solution

Let's solve some challenges

The challenges below are segregated by different difficulties. The repository also contains challenges grouped by problem type.

Some challenges may contain a reference to other challenges that should be solved before to have a better understanding of the problem. Check the look at problem-solving strategy .

Take your time before you view the presented solution. To succeed you need to practice often, repeat the same challenges multiple times and be persistent over time.

Good luck! 🤞

Beginner

Capitalize sentence
Get odd numbers
Range contains range?
Add up to
Linear search
Count down
Count up and down
Format train route
Generate all pairs
Count unique values
Print number
Print number with steps
Power
Factorial
Product
Capitalize first
Decapitalize const
Longest word
Reverse list

Intermediate

Is palindrome
Is tolerant palindrome
Is permutation palindrome
Is anagram
Max occurring char
String reverse
Find the vowels
Int reverse
Pyramid generator
Steps generator
Fizz Buzz
Caesar cipher
Has repeated char
Smallest elements
Largest elements

Advanced

Spiral matrix generator
Find rectangle
Queue
Combine queues
Stack
Bubble sort
Selection sort
Square equals
Sum zero
Digit frequency
Get duplicated arguments
Find pair with target average
Binary search tree
Tree traversal (breath first)
Tree traversal (depth first)
Tree level width
Binary search tree (insert)
Binary search tree (validate)
Any callback
Flatten
Binary search
Surrounded letter
Insertion sort
Quick sort
Radix sort
Doubly linked list
Max binary heap
Add numbers

Expert

Chunk
Singly linked list
Linked list midpoint
Circular check
Linked list take n-th element from last
Is sub string
Merge sort
Fibonacci
Fibonacci with recursive cache
Max sub list sum
Min sub list length
Subtract
Coins
Medan of sorted lists
LRU Cache
Advanced Cache

Troubleshoot

If you don't see the green play icon used to run the tests try to open Settings > Build, Execution, Deployment > Build tools > Gradle and set Gradle JVM to a different version.

Useful links

More coding challenges

Challenges

GeeksForGeeks - large and nicely segregated set of problems.
HackerRank - a large set of problems and additional interview problems for business.
LeetCode - data structures/algorithms/company interview problems segregated by difficulty.
Exercism - coding challenge website that offers MANY challenges spanning over 60 programming languages.
Project Euler - more complex challenges, usually related to mathematics. The site already contains 600+ problems and a new code challenge is available every week or two. You will probably have to discuss the problem with the community because solutions are not on the website.
Advent of code - one month of various programming problems released daily at the end of the year. Fortunately, archive of past events is still there.
CoderByte - 200+ challenges, data structures/algorithms/company interview problems segregated by difficulty. Unfortunately, most of them are only available for premium users. Premium gives you access to premium step-by-step solutions and user solutions.
CodeChef - contains a set of programming problems segregated by difficulty.
Code Forces - list of programming challenges is smaller than other websites, but you will still have plenty of problems to solve.
Spoj - list of programming challenges is smaller than other websites, but you will still have plenty of problems to solve.

Game challenges

CodeWars - solve visual challenges by writing code for the.
CodinGame - solve visual challenges by writing code for the.

Video courses

JavaScript Algorithms and Data Structures Masterclass
The Coding Interview Bootcamp Algorithms + Data Structures
Master the Coding Interview Data Structures + Algorithms
Learning Algorithms in JavaScript from Scratch
Data Structures and Algorithms Deep Dive Using Java

Books

Cracking the Coding Interview, 6th Edition
Algorithms, 4th Edition
Introduction to Algorithms, 3rd Edition (The MIT Press)
More books...

Websites

Hiring without whiteboards - listing of companies (or teams) that don't do "whiteboard" interviews.
VisuAlgo - visualizes data structures and algorithms through animations algorithms.
Data structures explained - description of various data structures.
Sorting algorithms animations - visually compares the most popular sorting algorithms using animations.
Big-O poster - time/space complexity poster to print and put on the wall.
Big-O Cheat Sheet - covers the space and time Big-O complexities of common algorithms.

Coding interview repositories

Coding Interview University
Awesome Interview Questions
Google Interview University
Interviews

Contribute

Feedback and new contributions are welcome whether it's through bug reports or new PRs. To add new coding challenges just follow this guide and open PR.

Author

License

MIT License

Copyright (c) 2023 Igor Wojda

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

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