Problem C. Palindrome subsequence
时间限制 1000 ms
内存限制 63.9990234375 MB
In mathematics, a subsequence is a sequence that can be derived from another sequence by deleting some elements without changing the order of the remaining elements. For example, the sequence <A, B, D> is a subsequence of <A, B, C, D, E, F>.
(http://en.wikipedia.org/wiki/Subsequence)
Given a string S, your task is to find out how many different subsequence of S is palindrome. Note that for any two subsequence X = <S
x1, S
x2, ..., S
xk> and Y = <S
y1, S
y2, ..., S
yk> , if there exist an integer i (1<=i<=k) such that xi != yi, the subsequence X and Y should be consider different even if S
xi = S
yi. Also two subsequences with different length should be considered different.
输入数据
输出数据
For each test case, output the case number first, then output the number of different subsequence of the given string, the answer should be module 10007.
样例输入
复制
4
a
aaaaa
goodafternooneveryone
welcometoooxxourproblems
样例输出
复制
Case 1: 1
Case 2: 31
Case 3: 421
Case 4: 960
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