Recursive strings output

Question

I have this code:

var al = ["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"];

function output(a, ind) {
    if (!ind) {
        ind = 0;
    }

    if (ind < 26) {
        var newtext = document.createTextNode(recursString(a[ind], ind));
        var br = document.createElement("br");
        var para = document.getElementById("hello");
        para.appendChild(newtext);
        para.appendChild(br);

        output(a, ++ind);
    }
}

var iter = 0;
var s = "";

function recursString(str, i) {
    if (i === 0) {
        s += str;

        return s;
    }

    if (iter < i) {
        s += str;
        iter++;

        recursString(str, i);
    }

    return s;
}

It outputs strings like this:

A
AB
ABC
ABCD
ABCDE
etc.

But i need:

A
BB
CCC
DDDD
EEEEE
etc.

I need to use only recursion. I suspect, according to debugging, s variable doesn't work like it should.. How do i fix it to make it work the way i want?

The variable s work like it should. You do not reset its value between each concatenation. You will need an other method that will be called i number of time to do your concatenation with the same character. — Patrick Desjardins
– Patrick Desjardins, Commented Nov 22, 2011 at 15:03

pimvdb · Accepted Answer · 2011-11-22 15:21:52Z

3

You should append the same letter each time, and stop when the length is the index of the letter in the alfabet + 1: http://jsfiddle.net/5h4sX/.

Note that you're currently changing the variables outside the function. You could also pass them along with each recursive call, but you don't need to if you want to keep it more understandable.

var str = "",
    iter = 0;

function recursString(letter, totalLength) {
    str += letter; // add letter

    if (iter === totalLength) { // stop recursing
        return str; // return what we have built up
    } else if (iter < totalLength) {
        iter++; // increment iteration variable
        return recursString(letter, totalLength); // return the result of a recursive call
    }
}

You do need to reset the variables before each recursive call though:

str = "";
iter = 0;
var newtext = document.createTextNode(
    recursString(a[ind], ind)
);

answered Nov 22, 2011 at 15:21

pimvdb

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3 Comments

DrStrangeLove Over a year ago

Thanks! But your jsfiddle is not correct. Every character should be repeated according to its place in alphabet. e.g. C - repeated 3 times, Z -26 times, H- 8 times etc.

DrStrangeLove Over a year ago

@mdmullinax thanks!! That's more like it!! i didnt recognise it was a right solution without css. Probably because of different widths of characters..

pimvdb Over a year ago

@DrStrangeLove: The fiddle does show three Cs and eight Hs etc. They don't have an increasing width but that's because of the font.

matehat · Accepted Answer · 2011-11-22 15:29:57Z

2

Forgetting about the global variables iter and str, you could replace the last function with :

function recursString(str, ind) {
  return ind == 0 ? str : str+recursString(str, --ind);
}

This can be rewritten in a more expanded form like this :

function recursString(str, ind) {
  if (ind == 0)
    return str;
  else {
    ind -= 1;
    return str + recursString(str, ind);
  }
}

edited Nov 22, 2011 at 15:29

answered Nov 22, 2011 at 15:21

matehat

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