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Language tracks
Crystal track
Exercises
Exercises on the Crystal track
Join the Crystal Track
50 exercises to help you master Crystal
easy
Hello World
The classical introductory exercise. Just say "Hello, World!"
misc
easy
Hamming
Calculate the Hamming difference between two DNA strands.
misc
easy
Gigasecond
Given a moment, determine the moment that would be after a gigasecond has passed.
misc
easy
RNA Transcription
Given a DNA strand, return its RNA Complement Transcription.
misc
easy
Bob
Bob is a lackadaisical teenager. In conversation, his responses are very limited.
misc
easy
Raindrops
Convert a number to a string, the content of which depends on the number's factors.
misc
easy
Leap
Given a year, report if it is a leap year.
misc
easy
Triangle
Determine if a triangle is equilateral, isosceles, or scalene.
misc
easy
Difference Of Squares
Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.
math
easy
Pangram
Determine if a sentence is a pangram.
misc
easy
Largest Series Product
Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.
math
easy
Matching Brackets
Make sure the brackets and braces all match.
misc
easy
Sieve
Use the Sieve of Eratosthenes to find all the primes from 2 up to a given number.
math
easy
Roman Numerals
Write a function to convert from normal numbers to Roman Numerals.
misc
easy
Atbash Cipher
Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.
misc
easy
Anagram
Given a word and a list of possible anagrams, select the correct sublist.
misc
easy
React
Implement a basic reactive system.
misc
easy
Acronym
Convert a long phrase to its acronym
misc
easy
Binary
Convert a binary number, represented as a string (e.g. '101010'), to its decimal equivalent using first principles
math
easy
Binary Search Tree
Insert and search for numbers in a binary tree.
algorithms
data structures
recursion
trees
easy
Run Length Encoding
Implement run-length encoding and decoding.
misc
easy
Pascal's Triangle
Compute Pascal's triangle up to a given number of rows.
math
easy
Forth
Implement an evaluator for a very simple subset of Forth
misc
easy
Flatten Array
Take a nested list and return a single list with all values except nil/null
misc
easy
Armstrong Numbers
Determine if a number is an Armstrong number
algorithms
loops
math
easy
Isogram
Determine if a word or phrase is an isogram.
algorithms
conditionals
loops
maps
strings
easy
Two Fer
Create a sentence of the form "One for X, one for me."
conditionals
optional values
text formatting
easy
Reverse String
Reverse a string
strings
easy
Collatz Conjecture
Calculate the number of steps to reach 1 using the Collatz conjecture
loops
math
easy
Scrabble Score
Given a word, compute the Scrabble score for that word.
games
loops
maps
strings
easy
Space Age
Given an age in seconds, calculate how old someone is in terms of a given planet's solar years.
conditionals
floating point numbers
integers
easy
ISBN Verifier
Check if a given string is a valid ISBN-10 number.
arrays
strings
medium
Grains
Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.
math
integers
medium
Perfect Numbers
Determine if a number is perfect, abundant, or deficient based on Nicomachus' (60 - 120 CE) classification scheme for natural numbers.
algorithms
filtering
integers
math
easy
Nth Prime
Given a number n, determine what the nth prime is.
algorithms
integers
math
easy
Resistor Color
Convert a resistor band's color to its numeric representation
arrays
strings
easy
Strain
Implement the `keep` and `discard` operation on collections. Given a collection and a predicate on the collection's elements, `keep` returns a new collection containing those elements where the predicate is true, while `discard` returns a new collection containing those elements where the predicate is false.
arrays
filtering
loops
easy
All Your Base
Convert a number, represented as a sequence of digits in one base, to any other base.
integers
math
transforming
easy
Luhn
Given a number determine whether or not it is valid per the Luhn formula.
algorithms
integers
strings
medium
Secret Handshake
Given a decimal number, convert it to the appropriate sequence of events for a secret handshake.
arrays
bitwise operations
integers
medium
Sum Of Multiples
Given a number, find the sum of all the multiples of particular numbers up to but not including that number.
integers
loops
math
easy
Darts
Write a function that returns the earned points in a single toss of a Darts game
conditionals
math
easy
Resistor Color Duo
Convert color codes, as used on resistors, to a numeric value.
arrays
strings
medium
Proverb
For want of a horseshoe nail, a kingdom was lost, or so the saying goes. Output the full text of this proverbial rhyme.
arrays
loops
strings
easy
Series
Given a string of digits, output all the contiguous substrings of length `n` in that string.
arrays
loops
enumerable
easy
Meetup
Calculate the date of meetups.
dates
time
transforming
type conversion
medium
Allergies
Given a person's allergy score, determine whether or not they're allergic to a given item, and their full list of allergies.
bitwise operations
enumeration
easy
Prime Factors
Compute the prime factors of a given natural number.
algorithms
integers
math
easy
Protein Translation
Translate RNA sequences into proteins.
filtering
maps
sequences
easy
ETL
We are going to do the `Transform` step of an Extract-Transform-Load.
loops
maps
transforming