### findLonelyPixel 
from typing import *
def f_gold(picture: List[List[str]]) -> int:
    m, n = len(picture), len(picture[0])
    rows, cols = [0] * m, [0] * n
    for i in range(m):
        for j in range(n):
            if picture[i][j] == 'B':
                rows[i] += 1
                cols[j] += 1
    res = 0
    for i in range(m):
        if rows[i] == 1:
            for j in range(n):
                if picture[i][j] == 'B' and cols[j] == 1:
                    res += 1
                    break
    return res