8月19日CCPC——A Secret（未解决）

Problem DescriptionToday is the birthday of SF,so VS gives two strings S1,S2 to SF as a present,which have a big secret.SF is interested in this secret and ask VS how to get it.There are the things that VS tell:  Suffix(S2,i) = S2[i...len].Ni is the times that Suffix(S2,i) occurs in S1 and Li is the length of Suffix(S2,i).Then the secret is the sum of the product of Ni and Li.  Now SF wants you to help him find the secret.The answer may be very large, so the answer should mod 1000000007. InputInput contains multiple cases.  The first line contains an integer T,the number of cases.Then following T cases.  Each test case contains two lines.The first line contains a string S1.The second line contains a string S2.  1<=T<=10.1<=|S1|,|S2|<=1e6.S1 and S2 only consist of lowercase ,uppercase letter. OutputFor each test case,output a single line containing a integer,the answer of test case.  The answer may be very large, so the answer should mod 1e9+7. Sample Input2aaaaaaaabababababa Sample Output1319Hintcase 2: Suffix(S2,1) = "aba",Suffix(S2,2) = "ba",Suffix(S2,3) = "a".N1 = 3,N2 = 3,N3 = 4.L1 = 3,L2 = 2,L3 = 1.ans = （3*3+3*2+4*1）%1000000007.

这道题就是找第二个字符串在第一个字符串中的子集的个数。

aaaaa

aa

4*2+5*1=13

一开始运用strstr函数，测试用例可以，但提交超时。

最后确认为用KMP来做，未果。

欢迎大神指点，欢迎大神提供答案和思路。