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.
思路：
不会做，动态规划的递推式子写不出来。看看这两篇博客吧。我的动态规划需要加强。
[leetcode] Distinct Subsequences
原文：http://www.cnblogs.com/jiasaidongqi/p/4235819.html