Orig Description
Score : 500 points
Problem StatementThere are 2N squares arranged from left to right. You are given a string of length 2N representing the color of each of the squares.
The color of the i-th square from the left is black if the i-th character of S is B, and white if that character is W.
You will perform the following operation exactly N times: choose two distinct squares, then invert the colors of these squares and the squares between them. Here, to invert the color of a square is to make it white if it is black, and vice versa.
Throughout this process, you cannot choose the same square twice or more. That is, each square has to be chosen exactly once.
Find the number of ways to make all the squares white at the end of the process, modulo 10^9+7.
Two ways to make the squares white are considered different if and only if there exists i (1 \leq i \leq N) such that the pair of the squares chosen in the i-th operation is different.
Constraints
1 \leq N \leq 10^5
|S| = 2N
Each character of S is B or W.
InputInput is given from Standard Input in the following format:
N
S
OutputPrint the number of ways to make all the squares white at the end of the process, modulo 10^9+7. If there are no such ways, print 0.
Sample Input 12
BWWB
Sample Output 14
There are four ways to make all the squares white, as follows:
Choose Squares 1, 3 in the first operation, and choose Squares 2, 4 in the second operation.
Choose Squares 2, 4 in the first operation, and choose Squares 1, 3 in the second operation.
Choose Squares 1, 4 in the first operation, and choose Squares 2, 3 in the second operation.
Choose Squares 2, 3 in the first operation, and choose Squares 1, 4 in the second operation.
Sample Input 24
BWBBWWWB
Sample Output 2288
Sample Input 35
WWWWWWWWWW
Sample Output 30
Extracted Specification
An integer N (1 ≤ N ≤ 10^5), representing some quantity or size.
A string S of length 2N, where each character is either 'B' or 'W'.
### Example Input:
```
2
BWWB
```
### Function Signature:
Write a function f(N, S) that takes in the input.
def f(N: int, S: str):
'''
N: an integer
S: a string
'''
Test Case Generator
Sure! Below is a Python function to generate test cases for the given problem statement.
```python
import random
def generate_test_case():
# Set the constraints
N = random.randint(1, 10**5)
S = ''.join(random.choice(['B', 'W']) for _ in range(2 * N))
return N, S
# Example usage
if __name__ == "__main__":
N, S = generate_test_case()
print(N)
print(S)
```
### Explanation
1. **N Generation**:
- `N` is randomly chosen between 1 and \(10^5\).
2. **String S Generation**:
- `S` is generated as a string of length `2N` where each character is randomly chosen to be either 'B' (black) or 'W' (white).
### Example Output
When you run the function, it will provide an output like:
```
74820
BWBWBWWBBWB...WWBWBWBW
```
This satisfies the constraints given in the problem statement.
### Note
Given the large possible values for `N`, running this in an environment with limited resources could take significant memory and time. For testing purposes, you may want to start with smaller values of `N` and verify the correctness of your solution incrementally with larger inputs.