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Programming Puzzle: String Length

February 21, 2012

Determine the length of a string without using any built-in .length or length getting functions.

Typical to true-engineering form, my first idea was overly complicated. I had reasoned that I could write a recursive loop to progressively build up a 2nd string, then compare them to see if the lengths matched. The problem there of course is that in order to do the comparison I have to use .length. #fail

After chuckling at myself for such an obvious oversight I realized there was a simpler solution. A string could be treated as an array, and the first character could simply be shifted off recursively and the length determined that way. A simpler implementation would be instead of converting the string to an array, simply using .substr(1).

function getStrLen (s) {
    var loop = function(acc, s) {
        if (s === “”) { return acc; }
        return loop(acc + 1, s.substr(1));
    return loop(0, s);

Now that I’ve gotten used to tail recursion, it seems that I’m seeing uses for it everywhere. I hope that’s a good thing…