PalindromePatterns | Topcoder Archive

Problem Statement

Using only the letters 'a' and 'b' return how many palindromes of length len do not have forbidden as a substring. A palindrome is a word that is unchanged by reversing it.

Definition

Class:: PalindromePatterns
Method:: howMany
Parameters:: String, int
Returns:: long
Method signature:: long howMany(String forbidden, int len)
(be sure your method is public)

Constraints

forbidden will contain between 1 and 5 characters inclusive.
len will be between 1 and 100 inclusive.
Each character in forbidden must be 'a' or 'b'.

Examples

```
"a"
```
```
5
```
```
Returns: 1
```
Only one possible palindrome.
```
"aaaaa"
```
```
5
```
```
Returns: 7
```
7 of the 8 possible palindromes work here.
```
"aa"
```
```
10
```
```
Returns: 8
```
```
"aa"
```
```
30
```
```
Returns: 987
```
```
"a"
```
```
1
```
```
Returns: 1
```

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