Algorithm that gives a certain permutation of letters from an input value

Question

I'm looking for a function that takes a certain input value and transforms it into a certain sequence of letters using the full alphabet.

This is the exact input: output I need:

5: aa
6: ab
7: ac
...
51: bu
52: bv
53: bw
...

And so on. And it should be able to continue with bigger input values creating combinations like aza, azb, azc or mnki, mnkj, mnkk.

Is this even possible, or do I just have to create all the permutations and store them? This would be easy, but memory intensive and slow and I don't need all permutations, just the one related to the input I'm giving.

Answer 1

Use base 26, interpreting the digits as a-z. You'll need to shift this to get 5 = aa.

def convert_to_base_26(number)
  return '' if number == 0
  number += 22
  base = 26
  digits = ('a'..'z').to_a

  result = ''
  while number > 0
    number -= 1
    digit = number % base
    result = digits[digit] + result
    number /= base
  end

  result
end


> convert_to_base_26(51)
=> "bu"
> convert_to_base_26(238_225)
=> "mnki"