santa_names.rb

def secret_santas(names)
  groups = names.map(&:split).group_by(&:last).values.sort_by(&:length).reverse
  santas = groups.flatten # list of names, most prolific first
  santees = santas.clone.shuffle # random for increased fun

  santas.map do |santa|
    santee = santees.find { |a| a.last != santa.last }
    raise "ran out of matches for #{name}" if santee.nil?
    
    santees.delete santee
    puts "#{santa.join(' ')} -> #{santee.join(' ')}"
  end
end