Buggy python submission (verdict: Time Limit Exceeded):
import numpy as np
n, m = map(int, input().split())
maze = np.array([list(input()) for _ in range(n)])
a = np.array(maze == "#")
ls = np.argwhere(a)
l = []
c= 0
while True:
  for i in [[1,0],[-1,0],[0,1],[0,-1]]:
    for j,k in ls + i:
      if -1<j<n and -1<k<m:
        if a[j,k] == False:
          a[j,k] = True
          l.append([j,k])
  ls = np.array(l)
  if l==[]:
    break
  l = []
  c += 1
print(c)

Fixed submission:
from collections import deque
n,m = map(int,input().split())

maze = [list(input()) for _ in range(n)]

def bfs():
    dx = (1, 0, -1, 0)
    dy = (0, 1, 0, -1)
    d = [([-1]*m)for _ in range(n)]
    q = deque([])
    for i in range(n):
        for j in range(m):
            if maze[i][j] == "#":
                d[i][j] = 0
                q.append((i,j))
    a = 0

    while q:
        x,y = q.popleft()
        for i in range(4):
            nx = x + dx[i]
            ny = y + dy[i]
            if 0<= nx < n and 0<= ny < m and maze[nx][ny] != '#' and d[nx][ny] == -1:
                q.append((nx,ny))
                d[nx][ny] = d[x][y] +1
                a = max(a,d[nx][ny])
    return a

print(bfs())

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
n,m = map(int,input().split())

maze = [list(input()) for _ in range(n)]

def bfs():
    dx = (1, 0, -1, 0)
    dy = (0, 1, 0, -1)
    d = [([-1]*m)for _ in range(n)]
    q = deque([])
    for i in range(n):
        for j in range(m):
            if maze[i][j] == "#":
                d[i][j] = 0
                q.append((i,j))
    a = 0

    while q:
        x,y = q.popleft()
        for i in range(4):
            nx = x + dx[i]
            ny = y + dy[i]
            if 0<= nx < n and 0<= ny < m and maze[nx][ny] != '#' and d[nx][ny] == -1:
                q.append((nx,ny))
                d[nx][ny] = d[x][y] +1
                a = max(a,d[nx][ny])
    return a

print(bfs())

Fixed submission:
from collections import deque
n,m = map(int,input().split())

maze = [list(input()) for _ in range(n)]

def bfs():
    dx = (1, 0, -1, 0)
    dy = (0, 1, 0, -1)
    d = [([-1]*m)for _ in range(n)]
    q = deque([])
    for i in range(n):
        for j in range(m):
            if maze[i][j] == "#":
                d[i][j] = 0
                q.append((i,j))
    a = 0

    while q:
        x,y = q.popleft()
        for i in range(4):
            nx = x + dx[i]
            ny = y + dy[i]
            if 0<= nx < n and 0<= ny < m and maze[nx][ny] != '#' and d[nx][ny] == -1:
                q.append((nx,ny))
                d[nx][ny] = d[x][y] +1
                a = max(a,d[nx][ny])
    return a

print(bfs())

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
n,m = map(int,input().split())

maze = [list(input()) for _ in range(n)]

def bfs():
    dx = (1, 0, -1, 0)
    dy = (0, 1, 0, -1)
    d = [([-1]*m)for _ in range(n)]
    q = deque([])
    for i in range(n):
        for j in range(m):
            if maze[i][j] == "#":
                d[i][j] = 0
                q.append((i,j))


    while q:
        x,y = q.popleft()
        for i in range(4):
            nx = x + dx[i]
            ny = y + dy[i]
            if 0<= nx < n and 0<= ny < m and maze[nx][ny] != '#' and d[nx][ny] == -1:
                q.append((nx,ny))
                d[nx][ny] = d[x][y] +1
    return max(sum(d,[]))

print(bfs())

Fixed submission:
from collections import deque
n,m = map(int,input().split())

maze = [list(input()) for _ in range(n)]

def bfs():
    dx = (1, 0, -1, 0)
    dy = (0, 1, 0, -1)
    d = [([-1]*m)for _ in range(n)]
    q = deque([])
    for i in range(n):
        for j in range(m):
            if maze[i][j] == "#":
                d[i][j] = 0
                q.append((i,j))
    a = 0

    while q:
        x,y = q.popleft()
        for i in range(4):
            nx = x + dx[i]
            ny = y + dy[i]
            if 0<= nx < n and 0<= ny < m and maze[nx][ny] != '#' and d[nx][ny] == -1:
                q.append((nx,ny))
                d[nx][ny] = d[x][y] +1
                a = max(a,d[nx][ny])
    return a

print(bfs())

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
n,m = map(int,input().split())
p = [input() for _ in range(n)]
q = deque([])
a = 0
for i in range(n):
    for j in range(m):
        if p[i][j] == "#":
            q.append((i,j))
for i in range(n):
    for j in range(m):
        a = max(min(abs(i-a)+abs(j-b)for a,b in q),a)
print(a)

Fixed submission:
from collections import deque
n,m = map(int,input().split())

maze = [list(input()) for _ in range(n)]

def bfs():
    dx = (1, 0, -1, 0)
    dy = (0, 1, 0, -1)
    d = [([-1]*m)for _ in range(n)]
    q = deque([])
    for i in range(n):
        for j in range(m):
            if maze[i][j] == "#":
                d[i][j] = 0
                q.append((i,j))
    a = 0

    while q:
        x,y = q.popleft()
        for i in range(4):
            nx = x + dx[i]
            ny = y + dy[i]
            if 0<= nx < n and 0<= ny < m and maze[nx][ny] != '#' and d[nx][ny] == -1:
                q.append((nx,ny))
                d[nx][ny] = d[x][y] +1
                a = max(a,d[nx][ny])
    return a

print(bfs())

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
n,m = map(int,input().split())

maze = [list(input()) for _ in range(n)]

def bfs():
    dx = (1, 0, -1, 0)
    dy = (0, 1, 0, -1)
    d = [([-1]*m)for _ in range(n)]
    q = deque([])
    for i in range(n):
        for j in range(m):
            if maze[i][j] == "#":
                d[i][j] = 0
                q.append((i,j))


    while q:
        x,y = q.popleft()
        for i in range(4):
            nx = x + dx[i]
            ny = y + dy[i]
            if 0<= nx < n and 0<= ny < m and maze[nx][ny] != '#' and d[nx][ny] == -1:
                q.append((nx,ny))
                d[nx][ny] = d[x][y] +1
    return max(sum(d,[]))

print(bfs())

Fixed submission:
from collections import deque
n,m = map(int,input().split())

maze = [list(input()) for _ in range(n)]

def bfs():
    dx = (1, 0, -1, 0)
    dy = (0, 1, 0, -1)
    d = [([-1]*m)for _ in range(n)]
    q = deque([])
    for i in range(n):
        for j in range(m):
            if maze[i][j] == "#":
                d[i][j] = 0
                q.append((i,j))
    a = 0

    while q:
        x,y = q.popleft()
        for i in range(4):
            nx = x + dx[i]
            ny = y + dy[i]
            if 0<= nx < n and 0<= ny < m and maze[nx][ny] != '#' and d[nx][ny] == -1:
                q.append((nx,ny))
                d[nx][ny] = d[x][y] +1
                a = max(a,d[nx][ny])
    return a

print(bfs())

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
n,m = map(int,input().split())

maze = [list(input()) for _ in range(n)]

def bfs():
    dx = (1, 0, -1, 0)
    dy = (0, 1, 0, -1)
    d = [([-1]*m)for _ in range(n)]
    q = deque([])
    for i in range(n):
        for j in range(m):
            if maze[i][j] == "#":
                d[i][j] = 0
                q.append((i,j))


    while q:
        x,y = q.popleft()
        if -1 in sum(d,[]):
            for i in range(4):
                nx = x + dx[i]
                ny = y + dy[i]
                if 0<= nx < n and 0<= ny < m and maze[nx][ny] != '#' and d[nx][ny] == -1:
                    q.append((nx,ny))
                    d[nx][ny] = d[x][y] +1
    return max(sum(d,[]))

print(bfs())

Fixed submission:
from collections import deque
n,m = map(int,input().split())

maze = [list(input()) for _ in range(n)]

def bfs():
    dx = (1, 0, -1, 0)
    dy = (0, 1, 0, -1)
    d = [([-1]*m)for _ in range(n)]
    q = deque([])
    for i in range(n):
        for j in range(m):
            if maze[i][j] == "#":
                d[i][j] = 0
                q.append((i,j))
    a = 0

    while q:
        x,y = q.popleft()
        for i in range(4):
            nx = x + dx[i]
            ny = y + dy[i]
            if 0<= nx < n and 0<= ny < m and maze[nx][ny] != '#' and d[nx][ny] == -1:
                q.append((nx,ny))
                d[nx][ny] = d[x][y] +1
                a = max(a,d[nx][ny])
    return a

print(bfs())