rubymathnumerical

Generate letters to represent number using ruby?

I would like to generate a sequence of letters i.e. "A", "DE" "GJE", etc. that correspond to a number. The first 26 are pretty easy so 3 returns "C", 26 returns "Z", and 27 would return "AA", 28 "AB", and so on.

The thing I can't quite figure out is how to do this so it will handle any number passed in. So if I pass in 4123 I should get back some combination of 3 letters since (26 * 26 * 26) allows for up to +17,000 combinations.

Any suggestions?

Solution 
  • class Numeric
  Alph = ("a".."z").to_a
  def alph
    s, q = "", self
    (q, r = (q - 1).divmod(26)); s.prepend(Alph[r]) until q.zero?
    s
  end
end

3.alph
# => "c"
26.alph
# => "z"
27.alph
# => "aa"
4123.alph
# => "fbo"