Given a string S and a string T, count the number of distinct subsequences of T in S.

A subsequence of a string is a new string which is formed from the original string by deleting some (can be none) of the characters without disturbing the relative positions of the remaining characters. (ie, "ACE" is a subsequence of "ABCDE" while "AEC" is not).

Here is an example:

S = "rabbbit", T = "rabbit"

Return 3.

class Solution {public:    int numDistinct(string s, string t) {        int l1 = s.length();        int l2 = t.length();                int dp[l1+1][l2+1];        for(int i=0;i