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Exercises
Exercises on the Ruby track
Join the Ruby Track
98 exercises to help you master Ruby
easy
Hello World
The classical introductory exercise. Just say "Hello, World!"
strings
easy
Two Fer
Create a sentence of the form "One for X, one for me."
strings
conditionals
easy
Resistor Color Duo
Convert color codes, as used on resistors, to a numeric value.
array
loops
easy
Acronym
Convert a long phrase to its acronym
regular expressions
strings
transforming
easy
High Scores
Manage a player's High Score list
arrays
medium
Matrix
Given a string representing a matrix of numbers, return the rows and columns of that matrix.
arrays
exception handling
matrices
strings
type conversion
easy
Series
Given a string of digits, output all the contiguous substrings of length `n` in that string.
arrays
loops
enumerable
easy
Word Count
Given a phrase, count the occurrences of each word in that phrase.
hash
loops
enumerable
easy
Hamming
Calculate the Hamming difference between two DNA strands.
strings
equality
loops
easy
Raindrops
Convert a number to a string, the content of which depends on the number's factors.
conditionals
filtering
strings
easy
Isogram
Determine if a word or phrase is an isogram.
sequences
strings
regular expressions
easy
Scrabble Score
Given a word, compute the Scrabble score for that word.
loops
maps
strings
easy
Luhn
Given a number determine whether or not it is valid per the Luhn formula.
algorithms
integers
strings
easy
Clock
Implement a clock that handles times without dates.
equality
text formatting
time
medium
Twelve Days
Output the lyrics to 'The Twelve Days of Christmas'
algorithms
pattern recognition
sequences
strings
text formatting
easy
Tournament
Tally the results of a small football competition.
integers
parsing
records
sorting
strings
text formatting
transforming
easy
Armstrong Numbers
Determine if a number is an Armstrong number
math
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.
algorithms
math
easy
Gigasecond
Given a moment, determine the moment that would be after a gigasecond has passed.
time
medium
Grains
Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.
bitwise operations
math
easy
RNA Transcription
Given a DNA strand, return its RNA Complement Transcription.
maps
transforming
easy
Robot Name
Manage robot factory settings.
randomness
easy
Pangram
Determine if a sentence is a pangram.
strings
loops
easy
Sieve
Use the Sieve of Eratosthenes to find all the primes from 2 up to a given number.
integers
algorithms
loops
sorting
math
easy
Roman Numerals
Write a function to convert from normal numbers to Roman Numerals.
numbers
transforming
easy
Nth Prime
Given a number n, determine what the nth prime is.
algorithms
integers
math
easy
Leap
Given a year, report if it is a leap year.
integers
booleans
conditionals
logic
easy
Bob
Bob is a lackadaisical teenager. In conversation, his responses are very limited.
strings
conditionals
medium
Run Length Encoding
Implement run-length encoding and decoding.
parsing
strings
transforming
easy
Accumulate
Implement the `accumulate` operation, which, given a collection and an operation to perform on each element of the collection, returns a new collection containing the result of applying that operation to each element of the input collection.
lists
medium
Sum Of Multiples
Given a number, find the sum of all the multiples of particular numbers up to but not including that number.
loops
math
medium
Grade School
Given students' names along with the grade that they are in, create a roster for the school
lists
sorting
structs
easy
Phone Number
Clean up user-entered phone numbers so that they can be sent SMS messages.
strings
conditionals
regular expressions
text formatting
transforming
easy
Prime Factors
Compute the prime factors of a given natural number.
integers
algorithms
math
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
medium
ETL
We are going to do the `Transform` step of an Extract-Transform-Load.
loops
maps
transforming
easy
Beer Song
Produce the lyrics to that beloved classic, that field-trip favorite: 99 Bottles of Beer on the Wall.
strings
loops
text formatting
medium
Bowling
Score a bowling game
algorithms
arrays
conditionals
easy
Space Age
Given an age in seconds, calculate how old someone is in terms of a given planet's solar years.
floating point numbers
if else statements
medium
Anagram
Given a word and a list of possible anagrams, select the correct sublist.
filtering
parsing
sorting
strings
medium
Binary Search Tree
Insert and search for numbers in a binary tree.
algorithms
recursion
searching
sorting
structs
trees
easy
Crypto Square
Implement the classic method for composing secret messages called a square code.
cryptography
filtering
strings
text formatting
transforming
medium
Alphametics
Write a function to solve alphametics puzzles.
algorithms
arrays
searching
medium
Rail Fence Cipher
Implement encoding and decoding for the rail fence cipher.
algorithms
cryptography
loops
sorting
strings
text formatting
transforming
medium
Nucleotide Count
Given a DNA string, compute how many times each nucleotide occurs in the string.
maps
parsing
strings
easy
Flatten Array
Take a nested list and return a single list with all values except nil/null
arrays
recursion
medium
Say
Given a number from 0 to 999,999,999,999, spell out that number in English.
numbers
strings
text formatting
transforming
easy
Meetup
Calculate the date of meetups.
dates
time
transforming
type conversion
medium
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.
booleans
errors
games
logic
medium
Palindrome Products
Detect palindrome products in a given range.
algorithms
math
medium
Matching Brackets
Make sure the brackets and braces all match.
parsing
strings
medium
Food Chain
Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'
conditionals
loops
recursion
strings
text formatting
medium
Saddle Points
Detect saddle points in a matrix.
arrays
integers
matrices
searching
easy
Triangle
Determine if a triangle is equilateral, isosceles, or scalene.
booleans
conditionals
logic
easy
Atbash Cipher
Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.
algorithms
cryptography
strings
transforming
medium
House
Output the nursery rhyme 'This is the House that Jack Built'.
recursion
strings
text formatting
medium
Secret Handshake
Given a decimal number, convert it to the appropriate sequence of events for a secret handshake.
arrays
bitwise operations
integers
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
medium
OCR Numbers
Given a 3 x 4 grid of pipes, underscores, and spaces, determine which number is represented, or whether it is garbled.
parsing
pattern recognition
medium
Pig Latin
Implement a program that translates from English to Pig Latin
conditionals
strings
transforming
medium
Simple Linked List
Write a simple linked list implementation that uses Elements and a List
arrays
loops
easy
Simple Cipher
Implement a simple shift cipher like Caesar and a more secure substitution cipher
algorithms
cryptography
interfaces
strings
transforming
easy
Wordy
Parse and evaluate simple math word problems returning the answer as an integer.
conditionals
integers
parsing
strings
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
medium
Poker
Pick the best hand(s) from a list of poker hands.
equality
games
parsing
pattern matching
sequences
strings
easy
Kindergarten Garden
Given a diagram, determine which plants each child in the kindergarten class is responsible for.
parsing
records
searching
strings
structs
easy
Largest Series Product
Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.
algorithms
integers
sequences
math
medium
Pythagorean Triplet
There exists exactly one Pythagorean triplet for which a + b + c = 1000. Find the product a * b * c.
algorithms
math
easy
Scale Generator
Generate musical scales, given a starting note and a set of intervals.
pattern matching
strings
easy
Protein Translation
Translate RNA sequences into proteins.
filtering
maps
sequences
medium
Perfect Numbers
Determine if a number is perfect, abundant, or deficient based on Nicomachus' (60 - 120 CE) classification scheme for positive integers.
algorithms
filtering
integers
math
medium
Circular Buffer
A data structure that uses a single, fixed-size buffer as if it were connected end-to-end.
queues
structs
medium
Diamond
Given a letter, print a diamond starting with 'A' with the supplied letter at the widest point.
algorithms
conditionals
loops
strings
text formatting
medium
Custom Set
Create a custom set type.
filtering
loops
sets
medium
Transpose
Take input text and output it transposed.
loops
strings
transforming
medium
Pascal's Triangle
Compute Pascal's triangle up to a given number of rows.
algorithms
arrays
recursion
math
medium
Linked List
Implement a doubly linked list
data structure
pointer
medium
Binary Search
Implement a binary search algorithm.
algorithms
arrays
searching
sorting
medium
Minesweeper
Add the numbers to a minesweeper board
arrays
games
loops
matrices
transforming
medium
Robot Simulator
Write a robot simulator.
concurrency
loops
sequences
strings
structs
easy
All Your Base
Convert a number, represented as a sequence of digits in one base, to any other base.
integers
transforming
math
hard
Connect
Compute the result for a game of Hex / Polygon
arrays
games
graphs
loops
searching
medium
Change
Correctly determine change to be given using the least number of coins
algorithms
arrays
loops
searching
easy
Collatz Conjecture
Calculate the number of steps to reach 1 using the Collatz conjecture
control flow loops
integers
conditionals
math
hard
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.
algorithms
floating point numbers
integers
lists
easy
Rotational Cipher
Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.
strings
cryptography
integers
easy
ISBN Verifier
Check if a given string is a valid ISBN-10 number.
arrays
medium
Dominoes
Make a chain of dominoes.
algorithms
arrays
searching
medium
Two Bucket
Given two buckets of different size, demonstrate how to measure an exact number of liters.
algorithms
conditionals
searching
easy
List Ops
Implement basic list operations
functional programming
lists
recursion
type conversion
easy
Affine Cipher
Create an implementation of the Affine cipher, an ancient encryption algorithm from the Middle East.
cryptography
strings
math
easy
Complex Numbers
Implement complex numbers.
math
medium
Zipper
Creating a zipper for a binary tree.
data structures
hard
Grep
Search a file for lines matching a regular expression pattern. Return the line number and contents of each matching line.
files
parsing
pattern matching
regular expressions
strings
text formatting
easy
Resistor Color
Convert a resistor band's color to its numeric representation
arrays
medium
Resistor Color Trio
Convert color codes, as used on resistors, to a human-readable label.
loops
easy
Darts
Write a function that returns the earned points in a single toss of a Darts game
math
geometry
easy
Microwave
math
strings
interpolation