LeetCode: Decode Ways

class Solution {
public:
    int dp[110];
    int numDecodings(string s) {
        int len = s.size();
        if(s[0] == '0') return 0;

        dp[0] = dp[1] = 1;
        for(int i=2;i<=len;i++){
            if(s[i-1] != '0')
                dp[i] += dp[i-1];
            if(i > 1 and ((s[i-2] == '1') or (s[i-2] == '2' and s[i-1] <= '6')))
                dp[i] += dp[i-2];
        }
        return dp[len];
    }
};