genetics.rb

  pop_with_fitness = population.map { |individual|
        [individual, individual.fitness]
      }

      Array.new(breeding_pool_size) do
        norm = pop_with_fitness.map(&:last).max

        if norm.zero?
          pop_with_fitness.pop.first
        else
          minimal_fitness = rand
          i = pop_with_fitness.find_index { |individual, fitness|
            fitness.fdiv(norm) >= minimal_fitness
          }

          pop_with_fitness.delete_at(i).first
        end
      end
    end
  end

  module TournamentSelection
    attr_accessor :tournament_size
    attr_accessor :base_probabiltty

    def select(population, breeding_pool_size)
      pop_with_fitness = population.map { |individual|
        [individual, individual.fitness]
      }.sort_by(&:last)

      base_probability = @base_probability || 1
      tournament_size  = @tournament_size  || 1

      Array.new(breeding_pool_size) do
        tournament = pop_with_fitness.sample(tournament_size).sort_by(&:last)
        chosen = tournament.reverse_each.find { |individual, _| p >= rand }
        chosen ||= tournament.first

        pop_with_fitness.delete(chosen)

        chosen.first
      end
    end
  end


end

class Problem
  def self.random_population(n)
    Array.new(n) { new(100*rand, 100*rand) }
  end

  def initialize(x, y)
    @x = x
    @y = y
  end

  attr_accessor :x, :y

  def fitness
    -(x - 5) ** 2 + (y - 7)**2 + 2*x + 3*y + 1000
  end
end

class Solution1 < Problem
  extend Genetics::RouletteWheelSelecion

  def self.test
    select(random_population(20), 5)
  end
end