onehundred.rb

def onehundred(arr)
  result = []
  arr.each_with_index do |x,i|
    i_of_2nd = arr[i..arr.length].find_index(100-x)
    if i_of_2nd
      result << [x, 100-x]
      arr.delete_at(i_of_2nd)
    end
  end
  return result
end