StringsBetween | Topcoder Archive

Problem Statement

All strings in this problem are strings of 0 to L lowercase English characters. We will call them valid strings.

All string comparisons are standard comparisons according to their lexicographic order: the string with a smaller character at the leftmost index on which they differ is smaller (e.g., "car" < "cat" because 'r' < 't') and if X is a prefix of Y, X is smaller than Y (e.g., "cat" < "cats").

You are given two valid strings A and B such that A < B.

Return the number of valid strings C such that A < C < B.

Definition

Class:: StringsBetween
Method:: count
Parameters:: int, String, String
Returns:: long
Method signature:: long count(int L, String A, String B)
(be sure your method is public)

Constraints

L will be between 0 and 10, inclusive.
A and B will be valid strings.
A will be less than B.

Examples

```
1
```
```
""
```
```
"d"
```
```
Returns: 3
```
The valid strings between "" and "d" are "a", "b", and "c".
```
2
```
```
"ay"
```
```
"c"
```
```
Returns: 28
```
The valid strings are "az", "b", "ba", "bb", ..., "bx", "by", "bz".
```
2
```
```
"ay"
```
```
"cb"
```
```
Returns: 30
```
Compared to the previous example we now also have valid strings "c" and "ca" within the specified range.
```
10
```
```
"bulldog"
```
```
"bulldozers"
```
```
Returns: 350592
```
```
4
```
```
"bx"
```
```
"fad"
```
```
Returns: 57028
```
```
4
```
```
"pier"
```
```
"pies"
```
```
Returns: 0
```

""

"zzzzzzzzzz"

Returns: 146813779479509

The largest possible output.

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