[백준] 토마토

문제
from collections import deque

n, m = map(int, input().split())
box = [list(map(int, input().split())) for _ in range(m)]

dx = [1, 0, -1, 0]
dy = [0, 1, 0, -1]

queue = deque()

for j in range(m):
    for i in range(n):
        if box[j][i] == 1:
            queue.append((i, j, 0))  

max_days = 0

while queue:
    x, y, day = queue.popleft()
    max_days = max(max_days, day)

    for i in range(4):
        nx, ny = x + dx[i], y + dy[i]
        if 0 <= nx < n and 0 <= ny < m and box[ny][nx] == 0:
            box[ny][nx] = 1
            queue.append((nx, ny, day + 1))

for row in box:
    if 0 in row:
        print(-1)
        break
else:
    print(max_days)
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