백준 7576번 - 토마토

from collections import deque

# 입력
m,n=map(int,input().split())
tomato = [list(map(int,input().split())) for _ in range(n)]
queue = deque([])  
dx = [-1,1,0,0]
dy = [0,0,-1,1]

# 처리
for i in range(n):
  for j in range(m):
    if tomato[i][j] == 1:
      queue.append([i,j])

def ripe():
  while queue:
    x,y = queue.popleft()
    
    for i in range(4):
      nx = x + dx[i]
      ny = y + dy[i]

      if 0<=nx<n and 0<=ny<m and tomato[nx][ny] == 0:
        tomato[nx][ny] = tomato[x][y] + 1
        queue.append([nx,ny])

ripe()
for i in range(n):
  for j in range(m):
    if tomato[i][j] == 0:
      print(-1)
      exit(0)
print(max(map(max, tomato))-1)