Buggy python submission (verdict: Runtime Error):
from collections import deque
H,W=map(int,input().split())

l=[input() for _ in range(H)]


def bfs(H,W,l):
  max_a,max_b=0,0
  que=deque()
  count=[[-1]*W for _ in range(H)]
  num=H*W
  dx=[1,-1,0,0]
  dy=[0,0,1,-1]
  for i in range(H):
    for j in range(W):
      if l[i][j]=='#':
        count[i][j]=0
        que.append([i,j])
        num-=1
  while num>0:
    x,y=que.popleft()
    for k in range(4):
      a,b=x+dx[k],y+dy[k]
      if a>=0 and a<H and b>=0 and b<W and count[a][b]==-1:
        count[a][b]=count[x][y]+1
        que.append([a,b])
        num-=1
        if num==0:
          max_x,max_y=a,b
  return count[max_x][max_y]
print(bfs(H,W,l))
    

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

l=[input() for _ in range(H)]


def bfs(H,W,l):
  ans=0
  que=deque()
  count=[[-1]*W for _ in range(H)]
  num=H*W
  dx=[1,-1,0,0]
  dy=[0,0,1,-1]
  for i in range(H):
    for j in range(W):
      if l[i][j]=='#':
        count[i][j]=0
        que.append([i,j])
        num-=1
  while num>0:
    x,y=que.popleft()
    for k in range(4):
      a, b=x+dx[k], y+dy[k]
      if a<0 or a>=H or b<0 or b>=W or count[a][b]!=-1:
        continue
      else:
        count[a][b]=count[x][y]+1
        que.append([a,b])
        num-=1
  for i in range(H):
    ans=max(ans,max(count[i]))
  return ans
print(bfs(H,W,l))

Buggy python submission (verdict: Runtime Error):
from collections import deque
H,W=map(int,input().split())

l=[input() for _ in range(H)]


def bfs(H,W,l):
  max_a,max_b=0,0
  que=deque()
  count=[[-1]*W for _ in range(H)]
  num=H*W
  dx=[1,-1,0,0]
  dy=[0,0,1,-1]
  for i in range(H):
    for j in range(W):
      if l[i][j]=='#':
        count[i][j]=0
        que.append([i,j])
        num-=1
  while num>0:
    x,y=que.popleft()
    for k in range(4):
      a,b=x+dx[k],y+dy[k]
      if a>=0 and a<H and b>=0 and b<W and count[a][b]==-1:
        count[a][b]=count[x][y]+1
        que.append([a,b])
        num-=1
        if num==0:
          max_x,max_y=a,b
  return count[max_x][max_y]
print(bfs(H,W,l))

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

l=[input() for _ in range(H)]


def bfs(H,W,l):
  ans=0
  que=deque()
  count=[[-1]*W for _ in range(H)]
  num=H*W
  dx=[1,-1,0,0]
  dy=[0,0,1,-1]
  for i in range(H):
    for j in range(W):
      if l[i][j]=='#':
        count[i][j]=0
        que.append([i,j])
        num-=1
  while num>0:
    x,y=que.popleft()
    for k in range(4):
      a, b=x+dx[k], y+dy[k]
      if a<0 or a>=H or b<0 or b>=W or count[a][b]!=-1:
        continue
      else:
        count[a][b]=count[x][y]+1
        que.append([a,b])
        num-=1
  for i in range(H):
    ans=max(ans,max(count[i]))
  return ans
print(bfs(H,W,l))

Buggy python submission (verdict: Runtime Error):
from collections import deque
H,W=map(int,input().split())

l=[input() for _ in range(H)]


def bfs(H,W,l):
  que=deque()
  count=[[-1]*W for _ in range(H)]
  num=H*W
  dx=[1,-1,0,0]
  dy=[0,0,1,-1]
  for i in range(H):
    for j in range(W):
      if l[i][j]=='#':
        count[i][j]=0
        que.append([i,j])
        num-=1
  while num>0:
    x,y=que.popleft()
    for k in range(4):
      a, b=x+dx[k], y+dy[k]
      if a<0 or a>=H or b<0 or b>=W or count[a][b]!=-1:
        continue
      else:
        count[a][b]=count[x][y]+1
        que.append([a,b])
        num-=1
        max_x=a
        max_y=b
  return count[max_x][max_y]
print(bfs(H,W,l))
    

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

l=[input() for _ in range(H)]


def bfs(H,W,l):
  ans=0
  que=deque()
  count=[[-1]*W for _ in range(H)]
  num=H*W
  dx=[1,-1,0,0]
  dy=[0,0,1,-1]
  for i in range(H):
    for j in range(W):
      if l[i][j]=='#':
        count[i][j]=0
        que.append([i,j])
        num-=1
  while num>0:
    x,y=que.popleft()
    for k in range(4):
      a, b=x+dx[k], y+dy[k]
      if a<0 or a>=H or b<0 or b>=W or count[a][b]!=-1:
        continue
      else:
        count[a][b]=count[x][y]+1
        que.append([a,b])
        num-=1
  for i in range(H):
    ans=max(ans,max(count[i]))
  return ans
print(bfs(H,W,l))

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

l=[input() for _ in range(H)]


def bfs(H,W,l):
  ans=0
  que=deque()
  count=[[-1]*W for _ in range(H)]
  num=H*W
  dx=[1,-1,0,0]
  dy=[0,0,1,-1]
  for i in range(H):
    for j in range(W):
      if l[i][j]=='#':
        count[i][j]=0
        que.append([i,j])
        num-=1
  while num>0:
    x,y=que.popleft()
    for k in range(4):
      a, b=x+dx[k], y+dy[k]
      if a<0 or a>=H or b<0 or b>=W or count[a][b]!=-1:
        continue
      else:
        count[a][b]=count[x][y]+1
        que.append([a,b])
        num-=1
  for i in range(H):
    ans=max(ans,max(count[i]))
  return ans
print(bfs(H,W,l))
    

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

l=[input() for _ in range(H)]


def bfs(H,W,l):
  ans=0
  que=deque()
  count=[[-1]*W for _ in range(H)]
  num=H*W
  dx=[1,-1,0,0]
  dy=[0,0,1,-1]
  for i in range(H):
    for j in range(W):
      if l[i][j]=='#':
        count[i][j]=0
        que.append([i,j])
        num-=1
  while num>0:
    x,y=que.popleft()
    for k in range(4):
      a, b=x+dx[k], y+dy[k]
      if a<0 or a>=H or b<0 or b>=W or count[a][b]!=-1:
        continue
      else:
        count[a][b]=count[x][y]+1
        que.append([a,b])
        num-=1
  for i in range(H):
    ans=max(ans,max(count[i]))
  return ans
print(bfs(H,W,l))