Grade School

grade_school.rb

class School
  
  def initialize
    @school = Hash.new { |school, grade| school[grade] = [] }
  end
  
  def to_h
    @school.sort.map { |grade, students| [grade, students.sort] }.to_h
  end
  
  def add(student, grade)
    @school[grade] << student
  end
  
  def grade(grade)
    @school[grade]
  end
end