Fastest function to generate Excel column letters in C#

Question

What is the fastest c# function that takes and int and returns a string containing a letter or letters for use in an Excel function? For example, 1 returns \"A\", 26 return

Answer 1

Once your function has run, let it cache the results into a dictionary. So that, it won't have to do the calculation again.

e.g. Convert(27) will check if 27 is mapped/stored in dictionary. If not, do the calculation and store "AA" against 27 in the dictionary.