http://play.codesthq.com/game#1

gistfile1.txt

# http://play.codesthq.com/game#1
# Write a method called format_number which converts given integer number to string like this:

# format_number(49)         #=> '49'
# format_number(12345)      #=> '12_345'
# format_number(-134567)    #=> '-134_567'
# format_number(1234567890) #=> '1_234_567_890'

# The idea is to create groups of 3 digits separated by '_' character.

def format_number(number)
  number_str = number.to_s.split('')
  result = []

  until number_str.empty? do
    result.unshift(number_str.pop(3).join())
  end

  if result[0] == "-"
    result[1].prepend(result.shift);
  end

  result.join("_")
end