Grade School

grade_school.rb

class School
attr_accessor :grades

  def initialize
    @grades = {}
  end

  def to_h
    grades.map { |grade, name| grades[grade] = name.sort }
    grades.sort.to_h
  end

  def add(name, grade)
    grades.has_key?(grade) ? self.grades[grade] << name : self.grades[grade] = [name]
  end

  def grade(grade)
    grades[grade].nil? ? [] : grades[grade]
  end
end