gistfile1.rb

arr = [1,2,3,4,5,5,6,7,7,7]
track = Hash.new
arr.each_with_index do | num, index |
  unless track[num]
   track[num] = Array.new
  end
  track[num].push(index)
end
track.each { |key, value|
  if value.count == 1
    puts "number: #{key} at index #{value}"
  end
}