115

class Solution {
public:
    int numDistinct(string s, string t) {
        int m=s.length(), n=t.length();
        unsigned long long int dp[m+1][n+1];
        memset(dp, 0, sizeof dp);
        for(int i=0; i<m; i++)
            dp[i][0] = 1;

        for(int i=1; i<=m; i++)
            for(int j=1; j<=n; j++){
                dp[i][j] = dp[i-1][j];
                if(s[i-1] == t[j-1])
                    dp[i][j] += dp[i-1][j-1];
            }
        return dp[m][n];
    }
};