DouKaku?

#! /usr/bin/ruby
    
class Text
    
    GOAL        = 'METHINKSITISAWEASEL'
    CHARACTER_SET = ('A'..'Z').to_a
    
    attr_accessor :text
    
    def create
        self.text = (1..GOAL.length).map { |_| CHARACTER_SET[rand(CHARACTER_SET.length)] }.to_s
        self
    end
    
    def update
        self.text[rand(GOAL.length)] = CHARACTER_SET[rand(CHARACTER_SET.length)]
        self
    end
    
    def rank
        self.text.split('').zip(GOAL.split('')).inject(0) { |r,s| s[0] == s[1] ? r + 1 : r }
    end
    
    def complete?
        self.rank == GOAL.length
    end
    
    def clone
        copy = super
        copy.text = self.text.clone
        copy
    end
end

class Processor
    
    POOL_SIZE    = 300
    COPY_SIZE    = 3
    
    attr_accessor :text_list
    
    def initialize
        self.text_list = (1..POOL_SIZE).map { |_| Text.new.create }.sort { |a,b| b.rank <=> a.rank }
        self
    end
    
    def process
        self.text_list = self.text_list.map { |t| (1..COPY_SIZE).map { |_| t.clone.update } }.flatten.sort { |a,b| b.rank <=> a.rank }.first(POOL_SIZE)
        self
    end
    
    def complete?
        self.text_list.first.complete?
    end
end

i = 1
processor = Processor.new
until processor.complete? do
    puts "process(#{i}): #{processor.text_list.first.text}(#{processor.text_list.first.rank})"
    processor.process
    i = i + 1
end
puts "complete(#{i}): #{processor.text_list.first.text}"