Find K’th Character of Decrypted String

find-k-char-encrypted-repeat-str.ts

function getCharAtPos(str, pos) {
    let letters = [];
    let repeats = 0;
    let positionToFind = pos;
    let currIndex = 0;
    for (const char of str) {
//         console.log({ char, letters, positionToFind, currIndex, repeats });
        currIndex++;
        if (char.match(/[a-z]/i)) {
            if (repeats > 0) {
                repeats = 0;
                letters = [];
            }
            letters.push(char);
            continue;
        }

        if (isNaN(+char)) {
            throw new Error('Unexpected character data type');
        }

        repeats *= 10;
        repeats += parseInt(char);
        if (!isNaN(+str[currIndex])) {
            continue;
        }

        const lettersCount = letters.length;
        const lettersRepeat = lettersCount * repeats;

        if (positionToFind <= lettersCount) {
            return letters[positionToFind - 1];
        }

        if (positionToFind > lettersRepeat) {
            positionToFind -= lettersRepeat;
            continue;
        }

        const charPos = positionToFind%lettersCount;
        
        return letters[charPos ? charPos - 1 : lettersCount-1];
    }
}