test.rb

require 'java'
require 'ruby-jgap'

# subclass JGAP::Problem
class MakeChangeProblem < JGAP::Problem

  population_size 500

  # define our solution chromosome
  chromosome do
    integer :quarters, min: 0, max: 3
    integer :dimes,    min: 0, max: 2
    integer :nickels,  min: 0, max: 1
    integer :pennies,  min: 0, max: 4
  end

  # define our fitness function
  fitness_function do |subject|
    target = 47 # goal: 47 cents
    q = read subject, :quarters
    d = read subject, :dimes
    n = read subject, :nickels
    p = read subject, :pennies
    
    coins = q + d + n + p
    value = 25*q + 10*d + 5*n + p
    delta = (target - value).abs # how far are we from our goal?
    
    minimize(coins + 2*delta)
  end


end

problem = MakeChangeProblem.new
problem.run(100) # 100 generations
problem.print_best