Function dfs

javascript/0091-decode-ways.js:21–31

(str, index, memo)

};

const dfs = (str, index, memo) => {
    let count = numDecodings(str, index + 1, memo);

    if (isTwoDigit(str, index)) {
        count += numDecodings(str, index + 2, memo);
    }

    memo.set(index, count);

    return count;
};

var isTwoDigit = (str, index) => {
    const twoDigit = Number(str.slice(index, index + 2));