CODEWITHSUNDEEP
javascriptnode.jsalgorithmgoogle-chromeecmascript-2016
Carl Johnson
Carl Johnson

Reputation: 23

JavaScript - Sequence of letters

I want to create the function which should return n-th string from the sequence

a, b, c, ... , z, aa, ab, ... , az, ba, ... , zz, aaa, ...

for given number n (indexes start from zero).

This is the current my function:

const charCode = 'a'.charCodeAt(0);

function identName(a){
  var b = '';

  while(a){
    b = String.fromCharCode(charCode + a % 26) + b;
    a = a / 26 | 0;
  }

  return b || 'a';
}

There are 26 letters, so I divide by 26 and each time I concatenate char code of remainder (modulo 26) to the string b. However this is the output:

a b c d e f g h i j k l m n o p q r s t u v w x y z ba bb bc bd be ...

As you can see, two letter strings starts from ba. I tried to decrease by 1 in each iteration, but then the result is like this:

a a b c d e f g h i j k l m n o p q r s t u v w x y a' aa ab ac ad ...

There are string a two times and there is no z. What am I doing wrong? How to properly generate this sequence in optimal and fast way?

Edit

I really don't see what is unclear in my question. I simply want a function which is called like this identName(0) and returns "a", when called like this identName(1) returns "b", etc..., when called like this: identName(26) returns "aa" and so on. How can it be described simplier. I really don't udnerstand what is unclear here... :/

Upvotes: 2

Views: 2561

Answers (1)

aduss
aduss

Reputation: 556

This should do the trick.

const charCode = 'a'.charCodeAt(0);

var identName = function (a) {
  var b = [a], sp, out, i, div;

    sp = 0;
    while(sp < b.length) {
        if (b[sp] > 25) {
            div = Math.floor(b[sp] / 26);
            b[sp + 1] = div - 1;
            b[sp] %= 26;
        }
        sp += 1;
    }

    out = "";
    for (i = 0; i < b.length; i += 1) {
        out = String.fromCharCode(charCode + b[i]) + out;
    }

    return out;
}

Essentially you were skipping over the 0 positions each time you got to the transition for example 27 -> 0,0 rather than 1,0.

Upvotes: 2

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