hamming_distance.rb

# `Coding Test : Hamming Distance
# Write a program that can calculate the Hamming distance between two DNA
#   strands.
#
# A mutation is simply a mistake that occurs during the creation or copying of a
#   nucleic acid, in particular DNA. Because nucleic acids are vital to cellular
#   functions, mutations tend to cause a ripple effect throughout the cell.
#   Although mutations are technically mistakes, a very rare mutation may equip
#   the cell with a beneficial attribute. In fact, the macro effects of
#   evolution are attributable by the accumulated result of beneficial
#   microscopic mutations over many generations.
#
# The simplest and most common type of nucleic acid mutation is a point
#   mutation, which replaces one base with another at a single nucleotide.
#
# By counting the number of differences between two homologous DNA strands taken
#   from different genomes with a common ancestor, we get a measure of the
#   minimum number of point mutations that could have occurred on the
#   evolutionary path between the two strands.
#
# This is called the “Hamming Distance”.
#
#    GAGCCTACTAACGGGAT
#    CATCGTAATGACGGCCT
#    ^ ^ ^  ^ ^    ^^
#
# The Hamming distance between these two DNA strands is 7.`
#
#
class HammingDistance
  def self.hammit(left, right)
    fail 'lengths don\'t match' if different_lengths?(left, right)

    (0..compare_length(left, right)).map { |index|
      left[index] == right[index]
    }.select { |result| result == false }.count
  end

  def self.compare_length(left, _)
    left.size
  end

  def self.different_lengths?(left, right)
    left.size != right.size
  end
end

left = 'GAGCCTACTAACGGGAT'
right = 'CATCGTAATGACGGCCT'

HammingDistance.hammit(left, right) == 7