Implement numbering scheme like A,B,C... AA,AB,... AAA..., similar to converting a number to radix26

Question

I want to implement numbering scheme like Microsoft Word uses for numbering. first one gets = A,next is B, next is C, .... then AA, then AB,....and so on. as shown below

 A      
 B
 C
 . 
 .
 AA
 AB
 AC
 .
 .
 AAA
 AAB
 ....

'=>' here means converted to.

some examples:

1 => A
26 => Z
27 => AA
52 => AZ
53 => BA

and heres the code for it:

   var convertToNumberingScheme = function(n){
        var x = n-1,
            r26 = x.toString(26),
            baseCharCode = "A".charCodeAt(0);

        var arr = r26.split(''),
            len = arr.length;

        var newArr =arr.map(function(val,i){
            val = parseInt(val,26);

            if( (i === 0) && ( len > 1)){
                val = val-1;
            }

            return String.fromCharCode(baseCharCode + val);
        });
        return newArr.join('');
    }

It seems to work fine, but any ideas if there are some potential bugs or ways to optimize this.

Answer 1

The function in the question converts to base 26, then splits the resulting string, and converts each digit back to decimal - and then to a letter. That seems roundabout.

Here's a simpler one:

function convertToNumberingScheme(number) {
  var baseChar = ("A").charCodeAt(0),
      letters  = "";

  do {
    number -= 1;
    letters = String.fromCharCode(baseChar + (number % 26)) + letters;
    number = (number / 26) >> 0; // quick `floor`
  } while(number > 0);

  return letters;
}

This function basically does a repeated "divmod" of the input number; getting the modulus 26 and the quotient (floor of n divided by 26). The modulus is converted to a A-Z character that's prepended to the output string, and the quotient is used as the input for the next iteration of the loop.