distribution.rb

class DistributeStudents
  attr_reader :coaches_to_students_distribution

  def initialize(coaches, students, coaches_to_students_distribution)
    @coaches = coaches
    @students = students
    @coaches_to_students_distribution = coaches_to_students_distribution
    @undistributed_students_size = students.size
    @number_of_students_per_coach = calculate_number_of_students_per_coach
  end

  def call
    @coaches.each do |coach|
      if @undistributed_students_size > @number_of_students_per_coach
        @coaches_to_students_distribution[coach] = @number_of_students_per_coach
      else
        @coaches_to_students_distribution[coach] = @undistributed_students_size
      end

      @undistributed_students_size -= @number_of_students_per_coach
    end

    return self
  end

  def calculate_number_of_students_per_coach
    total_students_size = @coaches_to_students_distribution.values.sum + @students.size
    number_of_students_per_coach = (total_students_size.to_f / @coaches.size.to_f).ceil
    number_of_students_per_coach -= 1 if number_of_students_per_coach * @coaches.size > total_students_size
    number_of_students_per_coach
  end
end


students = (1..20).to_a
coaches = (1..3).to_a
coaches_to_students_distribution = {}
distribute_students1 = DistributeStudents.new(coaches, students, coaches_to_students_distribution).call
puts distribute_students1.coaches_to_students_distribution.inspect


new_students = (20..30).to_a
distribute_students2 = DistributeStudents.new(coaches, new_students, distribute_students1.coaches_to_students_distribution).call
puts distribute_students2.coaches_to_students_distribution.inspect