String Transformations

string_transform.rb

# string_transform
# Usage:
# ruby string_transform.rb <target string>
#
# The hello world of genetic algorithms creates
# a random string and mutates it until it becomes
# the target string

def get_worth(item, target)
  sum = 0
  item.size.times do |i|
    sum += (item[i].ord - target[i].ord).abs
  end
  sum
end

def mutate(item)
  index = rand(item.size)
  new   = item.split("")
  new[index] = (rand(6) - 3 + new[index].ord).chr
  new[index] = (rand(6) - 3 + new[index].ord).chr
  new.join("")
end

def generate_initial(size)
  item = ""
  size.times do
    item += (rand(26) + 'a'.ord).chr
  end
  item
end

target  = ARGV[0]
current = generate_initial(target.size)
puts current

until get_worth(current, target) == 0
  new = mutate(current)
  new_worth  = get_worth(new, target)
  curr_worth = get_worth(current, target)
  current = (curr_worth < new_worth ? current : new)
  puts "#{current}: #{curr_worth}"
end