Get next alphabet string (exemples: 'A' -> 'B', 'Z' -> 'AA&-CodePudding

I'm trying to make a function that returns the next string. So if I input 'A' it returns 'B' etc. And i would like to pass as a parameter also an increment so 'AE' with an increment of 30 would be 'BI' and 'CM'(edit: it was 'CM' not 'ZM') would be 'AAQ'.

edit:

(input -> output)

Increment of 1

"A" -> "B"

"B" -> "C"

...

"Z" -> "AA"

...

"AZ" -> "BZ"

Increment of 30(the 30 is an example it can be anything)

"A" -> "AE"

"AE" -> "BI"

"BI" -> "CM"

"CM" -> "DQ"

Essentially, I want the next excel column. But i want to be able to increment. So with an increment of 30 i don't want the next one I want the 30 after if that makes sense.

CodePudding user response：

You're looking for an implementation of the bijective base 26 system, also known as "bijective hexavigesimal". There are many ways to do this; here's one possibility, involving converting such values to numbers before performing calculations on them, and then converting back from numbers afterward:

const baseCode = "A".charCodeAt(0) - 1;

function toBb26(n: number): string {
  let chars: string[] = [];
  while (n > 0) {
    const d = ((n - 1) % 26)   1;
    chars.unshift(String.fromCharCode(baseCode   d));
    n = (n - d) / 26;
  }
  return chars.join("");
}

function fromBb26(x: string): number {
  let ret = 0;
  for (const c of Array.from(x)) {
    ret *= 26;
    ret  = (c.charCodeAt(0) - baseCode);
  }
  return ret;
}

function increment(x: string, n: number=1) {
  return toBb26(fromBb26(x)   n);
}

console.log(increment("A")) // B
console.log(increment("AE", 30)) // BI
console.log(increment("ZM", 30)) // AAQ

I haven't rigorously tested this, and it might not be performance-optimized for your use case, and there are probably existing JS libraries that do this, etc. etc.

Playground link to code