hdu5651 xiaoxin juju needs help 组合数

xiaoxin juju needs help

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)
Total Submission(s): 594    Accepted Submission(s): 175

Problem Description

As we all known, xiaoxin is a brilliant coder. He knew **palindromic** strings when he was only a six grade student at elementry school.

This summer he was working at Tencent as an intern. One day his leader came to ask xiaoxin for help. His leader gave him a string and he wanted xiaoxin to generate palindromic strings for him. Once xiaoxin generates a different palindromic string, his leader will give him a watermelon candy. The problem is how many candies xiaoxin's leader needs to buy?

 

Input

This problem has multi test cases. First line contains a single integer  T(T≤20) which represents the number of test cases.
For each test case, there is a single line containing a string  S(1≤length(S)≤1,000).

 

Output

For each test case, print an integer which is the number of watermelon candies xiaoxin's leader needs to buy after mod  1,000,000,007.

 

Sample Input

3 aa aabb a

 

Sample Output

1 2 1

 

Source

BestCoder Round #77 (div.2)

无语了，求杨辉三角居然忘了注意边界C(n, 0) = 1，求的时候取模还不彻底，无语......失之毫厘谬以千里......

思路主要就是判断字符串长度的奇偶性，结合每个元素的奇偶性来判断有没有可能组成回文

如果可以的话然后利用组合数来算有多少种

比如

cccbba a abbccc

len = 13 但是实际上只要算len / 2 = 6也就是黑体的这一半的组合情况就行了，另外一半对称

算法是，如果取a,b,c的顺序，那么对于a:C(6, 1)，对于b去掉a占的位置:C(6 - 1, 2) = C(5, 2)

对于c去掉b, a占得位置:C(6 - 1 - 2, 3) = C(3, 3)

根据乘法原理ans = C(6, 1) * C(5, 2) * C(3, 3)

偶数情况以此类推

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