# R

When you're logged in, you can say `exercism fetch r` to get the next available exercise on the track.

Every time you submit a solution to an exercise, you will get the next in line the next time you fetch.

If you want to try a specific exercise, you can always fetch it directly (commands are listed below).

The exercises are ordered roughly in order of difficulty.

### Available Exercises

• Hello World The classical introductory exercise. Just say "Hello, World!"
• Leap Given a year, report if it is a leap year.
• Hamming Calculate the Hamming difference between two DNA strands.
• Rna Transcription Given a DNA strand, return its RNA Complement Transcription.
• Difference Of Squares Find the difference between the square of the sum and the sum of the squares of the first N natural numbers.
• Raindrops Convert a number to a string, the contents of which depend on the number's factors.
• Grains Calculate the number of grains of wheat on a chessboard given that the number on each square doubles.
• Bob Bob is a lackadaisical teenager. In conversation, his responses are very limited.
• Anagram Given a word and a list of possible anagrams, select the correct sublist.
• Space Age Given an age in seconds, calculate how old someone is in terms of a given planet's solar years.
• Sum Of Multiples Given a number, find the sum of all the multiples of particular numbers up to but not including that number.
• Word Count Given a phrase, count the occurrences of each word in that phrase.
• Phone Number Clean up user-entered phone numbers so that they can be sent SMS messages.
• Rotational Cipher Create an implementation of the rotational cipher, also sometimes called the Caesar cipher.
• Scrabble Score Given a word, compute the scrabble score for that word.
• Isogram Determine if a word or phrase is an isogram.
• Beer Song Produce the lyrics to that beloved classic, that field-trip favorite: 99 Bottles of Beer on the Wall.
• Perfect Numbers Determine if a number is perfect, abundant, or deficient based on Nicomachus' (60 - 120 CE) classification scheme for natural numbers.
• Prime Factors Compute the prime factors of a given natural number.
• Sieve Use the Sieve of Eratosthenes to find all the primes from 2 up to a given number.
• Largest Series Product Given a string of digits, calculate the largest product for a contiguous substring of digits of length n.
• Luhn Given a number determine whether or not it is valid per the Luhn formula.
• Secret Handshake Given a decimal number, convert it to the appropriate sequence of events for a secret handshake.
• Pascals Triangle Compute Pascal's triangle up to a given number of rows.
• Tournament Tally the results of a small football competition.
• Nucleotide Count Given a DNA string, compute how many times each nucleotide occurs in the string.
• Pangram Determine if a sentence is a pangram.
• Triangle Determine if a triangle is equilateral, isosceles, or scalene.
• Collatz Conjecture Calculate the number of steps to reach 1 using the Collatz conjecture
• Allergies Given a person's allergy score, determine whether or not they're allergic to a given item, and their full list of allergies.
• Crypto Square Implement the classic method for composing secret messages called a square code.
• Diamond Given a letter, print a diamond starting with 'A' with the supplied letter at the widest point.