weasel.rb

class Weazel
  CHARS = [*'A'..'Z', ' ']

  def initialize target
    @target = target
    @best = Array.new(28) { CHARS.sample }.join
  end

  def call
    0.upto Float::INFINITY do |n|
      puts "#{n}:\t#{@best}"
      break @best if @best == @target
      @best = find_highest_scored(new_generation(@best))
    end
  end
 
  def score_for_string str
    target_chars = @target.chars
    score = 0
    str.each_char.with_index do |char, index|
      score += 1 if char == target_chars[index]
    end

    score
  end

  def mutate_string string
    string.each_char.map { |char| rand(100) > 95 ? CHARS.sample : char }.join
  end

  def new_generation seed_str
    100.times.map { mutate_string(seed_str) }
  end
   
  def find_highest_scored generation
    generation.max_by { |str| score_for_string(str) }
  end
end

Weazel.new('METHINKS IT IS LIKE A WEASEL').call