### countUnguarded 
from typing import *
def f_gold(m: int, n: int, guards: List[List[int]], walls: List[List[int]]
) -> int:
    g = [[None] * n for _ in range(m)]
    for r, c in guards:
        g[r][c] = 'g'
    for r, c in walls:
        g[r][c] = 'w'
    for i, j in guards:
        for a, b in [[0, -1], [0, 1], [1, 0], [-1, 0]]:
            x, y = i, j
            while (
                0 <= x + a < m
                and 0 <= y + b < n
                and g[x + a][y + b] != 'w'
                and g[x + a][y + b] != 'g'
            ):
                x, y = x + a, y + b
                g[x][y] = 'v'
    return sum(not v for row in g for v in row)