add_spaces.coffee

assert = require 'assert'

reverse = (str) ->
  (str.split '').reverse().join ''

format = (num) ->
  reverse (reverse num.toString()).replace /\d{3}(?=\d)/g, '$& '

assert '1' is format 1
assert '10' is format 10
assert '100' is format 100
assert '1 000' is format 1000
assert '10 000' is format 10000
assert '100 000' is format 100000
assert '1 000 000' is format 1000000
assert '10 000 000' is format 10000000
assert '100 000 000' is format 100000000
assert '1 000 000 000' is format 1000000000