mentors.rb

mentors = ["Hans", "Ruedi"].shuffle
attendees = ["Klara", "Kevin", "Mike", "Sandro", "Sandy", "Silvan", "Lala"].shuffle
number_of_groups = (attendees.count / mentors.count)

groups = attendees.each_slice(number_of_groups).to_a

mentors.each_with_index do |mentor, index|
  puts "Group #{index + 1}: #{mentor}"
  puts "===================="
  puts groups.shift
  puts ""
end

unless groups.empty?
  puts "Leftovers"
  puts "===================="
  puts groups.shift
  puts ""
end