hyejjun.js

/**
 * @param {string} s
 * @return {number}
 */

var numDecodings = function (s) {
    if (s == null || s.length === 0) {
        return 0;
    }

    const n = s.length;
    const dp = new Array(n + 1).fill(0);
    dp[0] = 1;
    dp[1] = s[0] === '0' ? 0 : 1;

    for (let i = 2; i <= n; i++) {
        const oneDigit = parseInt(s.substring(i - 1, i));
        const twoDigits = parseInt(s.substring(i - 2, i));

        // Check if single digit decoding is possible
        if (oneDigit >= 1 && oneDigit <= 9) {
            dp[i] += dp[i - 1];
        }

        // Check if two digit decoding is possible
        if (twoDigits >= 10 && twoDigits <= 26) {
            dp[i] += dp[i - 2];
        }
    }

    return dp[n];
};


console.log(numDecodings("12"));
console.log(numDecodings("226"));
console.log(numDecodings("06"));

/*
시간 복잡도: O(n)
공간 복잡도: O(n)
*/