numDecodings = (s) => {
    const isBaseCase = !s.length || s[0] === '0';
    if (isBaseCase) return 0;

    return decode(s);
}
2 Pointer - previous + previousPrevious
Time O(N) | Space O(1)
https://leetcode.com/problems/decode-ways/
@param {string} s
@return {number}