# BOJ - 2638 - 치즈

Updated:

```
import sys
from collections import deque
dx = [0, 0, 1, -1]
dy = [1, -1, 0, 0]
def BFS(cheese, N, M):
dq = deque()
dq.append((0, 0))
air = [[-1] * M for _ in range(N)]
air[0][0] = 1
while dq:
x, y = dq.popleft()
for i in range(4):
nx = x + dx[i]
ny = y + dy[i]
if 0 <= nx < N and 0 <= ny < M:
if air[nx][ny] == -1:
if cheese[nx][ny] >= 1: cheese[nx][ny] += 1
else:
air[nx][ny] = 1
dq.append((nx, ny))
def solution():
N, M = map(int, sys.stdin.readline().split())
cheese = []
for _ in range(N):
cheese.append(list(map(int, input().split(' '))))
time = 0
while True:
BFS(cheese, N, M)
check = False
for i in range(N):
for j in range(M):
if cheese[i][j] >= 3:
cheese[i][j] = 0
check = True
elif cheese[i][j] == 2:
cheese[i][j] = 1
if not check: break
else: time += 1
print(time)
solution()
```

https://www.acmicpc.net/problem/2638

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