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 ls = s.length(), lt = t.length(), i, j;        vector
     
      
       > dp(lt+1, vector
       
        (ls+1, 0));        for(i = 0; i <= ls; i++)            dp[0][i] = 1;        for(i = 1; i <= lt; i++)        {            for(j = i; j <= ls; j++)            {                if(t[i-1] == s[j-1])                {                    dp[i][j] = dp[i-1][j-1]+dp[i][j-1];                }                else                {                    dp[i][j] = dp[i][j-1];                }            }        }        return dp[lt][ls];    }};
       
      
     

注意：

“bbb”和“”的匹配结果为1。所以第一行都为1。