AB | Topcoder Archive

Problem Statement

You are given two ints: N and K. Lun the dog is interested in strings that satisfy the following conditions:

The string has exactly N characters, each of which is either 'A' or 'B'.
The string s has exactly K pairs (i, j) (0 <= i < j <= N-1) such that s[i] = 'A' and s[j] = 'B'.

If there exists a string that satisfies the conditions, find and return any such string. Otherwise, return an empty string.

Definition

Class:: AB
Method:: createString
Parameters:: int, int
Returns:: String
Method signature:: String createString(int N, int K)
(be sure your method is public)

Constraints

N will be between 2 and 50, inclusive.
K will be between 0 and N(N-1)/2, inclusive.

Examples

```
3
```
```
2
```
```
Returns: "ABB"
```
This string has exactly two pairs (i, j) mentioned in the statement: (0, 1) and (0, 2).
```
2
```
```
0
```
```
Returns: "BA"
```
Please note that there are valid test cases with K = 0.
```
5
```
```
8
```
```
Returns: ""
```
Five characters is too short for this value of K.
```
10
```
```
12
```
```
Returns: "BAABBABAAB"
```
Please note that this is an example of a solution; other valid solutions will also be accepted.

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