### findBlackPixel 
from collections import defaultdict
from typing import *
def f_gold(picture: List[List[str]], target: int) -> int:
    m, n = len(picture), len(picture[0])
    rows = [0] * m
    cols = defaultdict(list)
    for i in range(m):
        for j in range(n):
            if picture[i][j] == 'B':
                rows[i] += 1
                cols[j].append(i)
    t = [[False] * m for _ in range(m)]
    for i in range(m):
        for k in range(i, m):
            if i == k:
                t[i][k] = True
            else:
                t[i][k] = all([picture[i][j] == picture[k][j] for j in range(n)])
            t[k][i] = t[i][k]
    res = 0
    for i in range(m):
        if rows[i] == target:
            for j in range(n):
                if len(cols[j]) == target and all([t[i][k] for k in cols[j]]):
                    res += 1
    return res