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Exercises
Exercises on the Haskell track
Join the Haskell Track
99 exercises to help you master Haskell
easy
Hello World
The classical introductory exercise. Just say "Hello, World!"
strings
easy
Leap
Given a year, report if it is a leap year.
booleans
easy
Space Age
Given an age in seconds, calculate how old someone is in terms of a given planet's solar years.
discriminated unions
easy
Pangram
Determine if a sentence is a pangram.
strings
easy
Bob
Bob is a lackadaisical teenager. In conversation, his responses are very limited.
strings
easy
Collatz Conjecture
Calculate the number of steps to reach 1 using the Collatz conjecture
maybe
number theory
math
easy
RNA Transcription
Given a DNA strand, return its RNA Complement Transcription.
either
easy
Nucleotide Count
Given a DNA string, compute how many times each nucleotide occurs in the string.
either
easy
Sum Of Multiples
Given a number, find the sum of all the multiples of particular numbers up to but not including that number.
number theory
math
easy
Grains
Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.
maybe
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.
number theory
math
easy
Acronym
Convert a long phrase to its acronym
strings
easy
Perfect Numbers
Determine if a number is perfect, abundant, or deficient based on Nicomachus' (60 - 120 CE) classification scheme for natural numbers.
maybe
number theory
math
easy
Hamming
Calculate the Hamming difference between two DNA strands.
maybe
easy
Grade School
Given students' names along with the grade that they are in, create a roster for the school
define type
easy
Isogram
Determine if a word or phrase is an isogram.
strings
easy
Diamond
Given a letter, print a diamond starting with 'A' with the supplied letter at the widest point.
strings
easy
ETL
We are going to do the `Transform` step of an Extract-Transform-Load.
algorithms
strings
easy
Raindrops
Convert a number to a string, the contents of which depend on the number's factors.
strings
easy
Resistor Color Duo
Convert color codes, as used on resistors, to a numeric value.
strings
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.
lazy evaluation
library reimplementation
filtering
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.
lazy evaluation
library reimplementation
easy
Phone Number
Clean up user-entered phone numbers so that they can be sent SMS messages.
maybe
easy
Twelve Days
Output the lyrics to 'The Twelve Days of Christmas'
strings
easy
ISBN Verifier
Check if a given string is a valid ISBN-10 number.
algorithms
easy
Run Length Encoding
Implement run-length encoding and decoding.
algorithms
strings
easy
Beer Song
Produce the lyrics to that beloved classic, that field-trip favorite: 99 Bottles of Beer on the Wall.
refactoring
easy
Triangle
Determine if a triangle is equilateral, isosceles, or scalene.
number theory
math
easy
Scrabble Score
Given a word, compute the scrabble score for that word.
misc
easy
Kindergarten Garden
Given a diagram, determine which plants each child in the kindergarten class is responsible for.
define type
easy
Complex Numbers
Implement complex numbers.
define type
number theory
math
easy
Robot Simulator
Write a robot simulator.
define type
easy
Secret Handshake
Given a decimal number, convert it to the appropriate sequence of events for a secret handshake.
bitwise operations
easy
Protein Translation
Translate RNA sequences into proteins.
maybe
easy
D&D Character
Randomly generate Dungeons & Dragons characters
random
medium
Anagram
Given a word and a list of possible anagrams, select the correct sublist.
filtering
lists
strings
medium
Simple Linked List
Write a simple linked list implementation that uses Elements and a List
define type
library reimplementation
medium
List Ops
Implement basic list operations
accumulator strictness
library reimplementation
filtering
medium
Meetup
Calculate the date of meetups.
misc
medium
Roman Numerals
Write a function to convert from normal numbers to Roman Numerals.
maybe
medium
Prime Factors
Compute the prime factors of a given natural number.
number theory
math
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.
algorithms
bitwise operations
medium
All Your Base
Convert a number, represented as a sequence of digits in one base, to any other base.
either
math
medium
Largest Series Product
Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.
either
math
medium
Clock
Implement a clock that handles times without dates.
define type
instance num
medium
Matrix
Given a string representing a matrix of numbers, return the rows and columns of that matrix.
define type
medium
House
Output the nursery rhyme 'This is the House that Jack Built'.
refactoring
medium
Pascal's Triangle
Compute Pascal's triangle up to a given number of rows.
number theory
math
medium
Pythagorean Triplet
There exists exactly one Pythagorean triplet for which a + b + c = 1000. Find the product a * b * c.
number theory
math
medium
Saddle Points
Detect saddle points in a matrix.
misc
medium
Series
Given a string of digits, output all the contiguous substrings of length `n` in that string.
lists
strings
medium
Sieve
Use the Sieve of Eratosthenes to find all the primes from 2 up to a given number.
number theory
math
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.
lists
recursion
medium
Binary Search
Implement a binary search algorithm.
maybe
medium
Atbash Cipher
Create an implementation of the atbash cipher, an ancient encryption system created in the Middle East.
algorithms
strings
medium
Matching Brackets
stack
medium
Crypto Square
Implement the classic method for composing secret messages called a square code.
misc
medium
Nth Prime
Given a number n, determine what the nth prime is.
maybe
number theory
math
medium
Word Count
Given a phrase, count the occurrences of each word in that phrase.
strings
medium
Binary Search Tree
Insert and search for numbers in a binary tree.
define type
maybe
medium
Luhn
Given a number determine whether or not it is valid per the Luhn formula.
algorithms
strings
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.
maybe
medium
OCR Numbers
Given a 3 x 4 grid of pipes, underscores, and spaces, determine which number is represented, or whether it is garbled.
strings
medium
Food Chain
Generate the lyrics of the song 'I Know an Old Lady Who Swallowed a Fly'
refactoring
medium
Rotational Cipher
Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.
strings
medium
Spiral Matrix
Given the size, return a square matrix of numbers in spiral order.
lists
medium
Custom Set
Create a custom set type.
define type
library reimplementation
medium
Parallel Letter Frequency
Count the frequency of letters in texts using parallel computation.
strings
medium
Transpose
Take input text and output it transposed.
lists
medium
Simple Cipher
Implement a simple shift cipher like Caesar and a more secure substitution cipher
io monad
mutable state
random
medium
Palindrome Products
Detect palindrome products in a given range.
math
lists
maybe
medium
Robot Name
Manage robot factory settings.
define type
io monad
random
medium
Pig Latin
Implement a program that translates from English to Pig Latin
strings
medium
Say
Given a number from 0 to 999,999,999,999, spell out that number in English.
maybe
medium
Bank Account
Simulate a bank account supporting opening/closing, withdraws, and deposits of money. Watch out for concurrent transactions!
define type
io monad
maybe
mutable state
medium
Sublist
Write a function to determine if a list is a sublist of another list.
misc
medium
Rail Fence Cipher
Implement encoding and decoding for the rail fence cipher.
algorithms
strings
medium
Linked List
Implement a doubly linked list
define type
io monad
library reimplementation
maybe
mutable state
medium
Zebra Puzzle
Solve the zebra puzzle.
algorithms
logic
medium
Minesweeper
Add the numbers to a minesweeper board
misc
medium
Wordy
Parse and evaluate simple math word problems returning the answer as an integer.
maybe
medium
Change
Correctly determine change to be given using the least number of coins
maybe
medium
Alphametics
Write a function to solve alphametics puzzles.
maybe
medium
Bowling
Score a bowling game
either
medium
Poker
Pick the best hand(s) from a list of poker hands.
maybe
hard
Connect
Compute the result for a game of Hex / Polygon
maybe
hard
Dominoes
Make a chain of dominoes.
maybe
hard
SGF Parsing
Parsing a Smart Game Format string.
maybe
hard
Go Counting
Count the scored points on a Go board.
maybe
hard
Lens Person
Use lenses to update nested records (specific to languages with immutable data).
lens
hard
Zipper
Creating a zipper for a binary tree.
define type
maybe
hard
Forth
Implement an evaluator for a very simple subset of Forth
define type
either
stack
hard
POV
Reparent a graph on a selected node
maybe