Crystal

via Exercism

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Provider

Exercism
Pricing

Free Online Course
Languages

English
Sessions

Self-Paced
Level

Intermediate

Found in

Crystal is a compiled language that is currently in the alpha stages of development. These are some of the language's goals: Ruby-inspired syntax. Statically type-checked but without having to specify the type of variables or method arguments.

Syllabus

Hello World

Exercism's classic introductory exercise. Just say "Hello, World!".

Ary's Amazing Lasagna

Learn about the basics of Crystal by following a lasagna recipe.

Crystal Hunter

Learn about booleans by implementing the rules of the Crystal Hunter game.

Wellington's Weather Station

Learn about numbers by update Wellington's weather station temperature system

Navigation Computer

Learn about number types while building a navigation system for ESA (Exercism Space Agency).

Johannes' Juice Maker

Help Johannes with their juice maker while learning about classes

Party Robot

Learn about strings by programming a party robot.

Weighing Machine

Learn about getter and setters by implementing a weighing machine.

High School Sweetheart

Learn about strings by helping high school sweethearts profess their love on social media via ASCII art.

Meltdown Mitigation

Learn about conditionals and avoid a meltdown by developing a simple control system for a Nuclear Reactor.

Interest is Interesting

Learn about while loops by adding interest to savings accounts.

Chess Game

Learn about ranges while making a chess game.

Library of Luton

Help the library of Luton to automate some of their processes, while learning about Chars

Bellebrook Basket League

Learn about modules, while building a basketball league ticketing system.

Castle Dinner

Learn about Nil while making sure no food or drink includes poison.

Password Lock

Build a password lock system while learning about union types

Blackjack

Learn about cases while simulating blackjack

Language List

Learn about arrays by keeping track of the programming languages you're currently learning on Exercism.

Chaitanas Colossal Coaster

Learn useful array methods helping Chaitana manage the lines for her colossal roller coaster.

the-farm

Learn about error handling in Crystal while feeding cows on the farm.

Foto Fusionist

Help the your friend develop Foto Fusionist, while learning about Binary, Octal, and Hexadecimal

Secrets

Learn about bit manipulation by writing a program to decrypt a message.

Task Handler

Learn about Procs & blocks by implementing a simple task handler.

spellbound-steel

Learn about Iteration by implementing methods to aid in the game of Spellbound Steel.

Kitchen Calculator

Learn about tuples and symbols by converting common US baking measurements to the metric system.

Acronym

Convert a long phrase to its acronym.

Anagram

Find the words that use the same letters as another word.

Armstrong Numbers

Determine if a number is an Armstrong number.

Atbash Cipher

Create an implementation of the Atbash cipher, an ancient encryption system created in the Middle East.

Bob is a lackadaisical teenager. In conversation, his responses are very limited.

Collatz Conjecture

Calculate the number of steps to reach 1 using the Collatz conjecture.

Difference of Squares

Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.

Change the data format for scoring a game to more easily add other languages.

Flatten Array

Take a nested list and return a single list with all values except nil/null.

Gigasecond

Given a moment, determine the moment that would be after a gigasecond has passed.

Hamming

Calculate the Hamming distance between two DNA strands.

Isogram

Determine whether a phrase is an isogram, a word with no repeated letters.

Leap

Determine whether a given year is a leap year.

Matching Brackets

Make sure the brackets and braces all match.

Pangram

Determine whether a phrase uses every letter in the Latin alphabet.

Raindrops

Convert a number into its corresponding raindrop sounds - Pling, Plang and Plong.

Resistor Color

Convert a resistor band's color to its numeric representation.

Resistor Color Duo

Convert color codes, as used on resistors, to a numeric value.

Reverse String

Reverse a given string.

Rotational Cipher

Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.

RNA Transcription

Given a DNA strand, return its RNA complement.

Run-Length Encoding

Implement run-length encoding and decoding.

Scrabble Score

Given a word, compute the Scrabble score for that word.

Triangle

Determine if a triangle is equilateral, isosceles, or scalene.

Darts

Calculate the points scored in a single toss of a Darts game.

Two Fer

Create a sentence of the form "One for X, one for me.".

Resistor Color Trio

Convert color codes, as used on resistors, to a human-readable label.

Space Age

Given an age in seconds, calculate how old someone is in terms of a given planet's solar years.

Resistor Color Expert

Convert color codes as used on resistors with different bands to a human-readable label.

ISBN Verifier

Check if a given string is a valid ISBN-10 number.

Luhn

Given a number determine whether or not it is valid per the Luhn formula.

Binary Search

Implement a binary search algorithm.

Phone Number

Clean up user-entered phone numbers so that they can be sent SMS messages.

Nucleotide Count

Given a DNA string, compute how many times each nucleotide occurs in the string.

Line Up

Help lining up customers at Yaʻqūb's Deli.

Roman Numerals

Convert modern Arabic numbers into Roman numerals.

High Scores

Manage a player's High Score list.

Perfect Numbers

Determine if a number is perfect, abundant, or deficient based on Nicomachus' (60 - 120 CE) classification scheme for positive integers.

Grains

Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.

Secret Handshake

Given a decimal number, convert it to the appropriate sequence of events for a secret handshake.

Bottle Song

Produce the lyrics to the popular children's repetitive song: Ten Green Bottles.

Clock

Implement a clock that handles times without dates.

All Your Base

Convert a number, represented as a sequence of digits in one base, to any other base.

Largest Series Product

Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.

Pascal's Triangle

Compute Pascal's triangle up to a given number of rows.

Sieve

Use the Sieve of Eratosthenes to find all the primes from 2 up to a given number.

Wordy

Parse and evaluate simple math word problems returning the answer as an integer.

Saddle Points

Detect saddle points in a matrix.

Nth Prime

Given a number n, determine what the nth prime is.

Prime Factors

Compute the prime factors of a given natural number.

Protein Translation

Translate RNA sequences into proteins.

Series

Given a string of digits, output all the contiguous substrings of length `n` in that string.

Sublist

Determine if a list is a sublist of another list.

Word Count

Given a phrase, count the occurrences of each word in that phrase.

Matrix

Given a string representing a matrix of numbers, return the rows and columns of that matrix.

Queen Attack

Given the position of two queens on a chess board, indicate whether or not they are positioned so that they can attack each other.

Affine Cipher

Create an implementation of the Affine cipher, an ancient encryption algorithm from the Middle East.

Kindergarten Garden

Given a diagram, determine which plants each child in the kindergarten class is responsible for.

Eliud's Eggs

Help Eliud count the number of eggs in her chicken coop by counting the number of 1 bits in a binary representation.

Proverb

For want of a horseshoe nail, a kingdom was lost, or so the saying goes. Output the full text of this proverbial rhyme.

Tournament

Tally the results of a small football competition.

Circular Buffer

A data structure that uses a single, fixed-size buffer as if it were connected end-to-end.

Crypto Square

Implement the classic method for composing secret messages called a square code.

Transpose

Take input text and output it transposed.

Yacht

Score a single throw of dice in the game Yacht.

Spiral Matrix

Given the size, return a square matrix of numbers in spiral order.

Split-Second Stopwatch

Keep track of time through a digital stopwatch.

Baffling Birthdays

Estimate the birthday paradox's probabilities.

Food Chain

Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'.

Camicia

Simulate the card game and determine whether the match ends or enters an infinite loop.

Robot Simulator

Write a robot simulator.

Relative Distance

Given a family tree, calculate the degree of separation.

Flower Field

Mark all the flowers in a garden.

Intergalactic Transmission

Add parity bits to a message for transmission

Forth

Implement an evaluator for a very simple subset of Forth.

Swift Scheduling

Convert delivery date descriptions to actual delivery dates.

Grade School

Given students' names along with the grade that they are in, create a roster for the school.

Meetup

Calculate the date of meetups.

Killer Sudoku Helper

Write a tool that makes it easier to solve Killer Sudokus

Strain

Implement the `keep` and `discard` operation on collections.

Bank Account

Simulate a bank account supporting opening/closing, withdraws, and deposits of money. Watch out for concurrent transactions!

Palindrome Products

Detect palindrome products in a given range.

Linked List

Implement a doubly linked list.

Allergies

Given a person's allergy score, determine whether or not they're allergic to a given item, and their full list of allergies.

Pig Latin

Implement a program that translates from English to Pig Latin.

Diamond

Given a letter, print a diamond starting with 'A' with the supplied letter at the widest point.

Custom Set

Create a custom set type.

Rail Fence Cipher

Implement encoding and decoding for the rail fence cipher.

Rational Numbers

Implement rational numbers.

Bowling

Score a bowling game.

Knapsack

Given a knapsack that can only carry a certain weight, determine which items to put in the knapsack in order to maximize their combined value.

Variable Length Quantity

Implement variable length quantity encoding and decoding.

Rectangles

Count the rectangles in an ASCII diagram.

Grep

Search a file for lines matching a regular expression pattern.

Complex Numbers

Implement complex numbers.

Word Search

Create a program to solve a word search puzzle.

Markdown

Refactor a Markdown parser.

Sum of Multiples

Given a number, find the sum of all the multiples of particular numbers up to but not including that number.

Pythagorean Triplet

Given an integer N, find all Pythagorean triplets for which a + b + c = N.

State of Tic-Tac-Toe

Determine the game state of a match of Tic-Tac-Toe.

Change

Correctly determine change to be given using the least number of coins.

Parallel Letter Frequency

Count the frequency of letters in texts using parallel computation.

Dominoes

Make a chain of dominoes.

OCR Numbers

Given a 3 x 4 grid of pipes, underscores, and spaces, determine which number is represented, or whether it is garbled.

Conway's Game of Life

Implement Conway's Game of Life.

Poker

Pick the best hand(s) from a list of poker hands.

Connect

Compute the result for a game of Hex / Polygon.

React

Implement a basic reactive system.

Given a number from 0 to 999,999,999,999, spell out that number in English.

Two Bucket

Given two buckets of different size, demonstrate how to measure an exact number of liters.

Binary Search Tree

Insert and search for numbers in a binary tree.

Alphametics

Given an alphametics puzzle, find the correct solution.

Simple Cipher

Implement the Vigenère cipher, a simple substitution cipher.

Book Store

To try and encourage more sales of different books from a popular 5 book series, a bookshop has decided to offer discounts of multiple-book purchases.