Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
h, w = map(int,input().split())
graph = []
finished = [[False for _ in range(w)] for _ in range(h)]
y = [0, 0, 1,-1]
x = [1,-1, 0, 0]
q = deque([])
for i in range(h):
    a = input()
    graph.append(a)
    for j in range(w):
        if a[j] == "#":
            q.append((i,j,0))
while q:
    c = q.popleft()
    for i in range(4):
        nh = c[0]+y[i]
        nw = c[1]+x[i]
        if nh < 0 or nh >= h or nw < 0 or nw >= w or finished[nh][nw]:continue
        finished[nh][nw] = True
        q.append((nh,nw,c[2]+1))
print(c[2])

Fixed submission:
from collections import deque
h, w = map(int,input().split())
graph = []
finished = [[False for _ in range(w)] for _ in range(h)]
y = [0, 0, 1,-1]
x = [1,-1, 0, 0]
q = deque([])
for i in range(h):
    a = input()
    graph.append(a)
    for j in range(w):
        if a[j] == "#":
            q.append((i,j,0))
while q:
    c = q.popleft()
    for i in range(4):
        nh = c[0]+y[i]
        nw = c[1]+x[i]
        if nh < 0 or nh >= h or nw < 0 or nw >= w or graph[nh][nw] == "#" or finished[nh][nw]:continue
        finished[nh][nw] = True
        q.append((nh,nw,c[2]+1))
print(c[2])

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
h, w = map(int,input().split())
graph = []
finishied = [[False for _ in range(w)] for _ in range(h)]
y = [0, 0, 1,-1]
x = [1,-1, 0, 0]
q = deque([])
for i in range(h):
    a = input()
    graph.append(list(a))
    for j in range(w):
        if a[j] == "#":
            q.append((i,j,0))
while q:
    c = q.popleft()
    for i in range(4):
        nh = c[0]+y[i]
        nw = c[1]+x[i]
        if nh < 0 or nh >= h or nw < 0 or nw >= w or graph[nh][nw] == "#":continue
        graph[nh][nw] = "#"
        q.append((nh,nw,c[2]+1))
print(c[2])

Fixed submission:
from collections import deque
h, w = map(int,input().split())
graph = []
finished = [[False for _ in range(w)] for _ in range(h)]
y = [0, 0, 1,-1]
x = [1,-1, 0, 0]
q = deque([])
for i in range(h):
    a = input()
    graph.append(a)
    for j in range(w):
        if a[j] == "#":
            q.append((i,j,0))
while q:
    c = q.popleft()
    for i in range(4):
        nh = c[0]+y[i]
        nw = c[1]+x[i]
        if nh < 0 or nh >= h or nw < 0 or nw >= w or graph[nh][nw] == "#" or finished[nh][nw]:continue
        finished[nh][nw] = True
        q.append((nh,nw,c[2]+1))
print(c[2])

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
h, w = map(int,input().split())
graph = [list(input()) for _ in range(h)]
finishied = [[False for _ in range(w)] for _ in range(h)]
y = [0, 0, 1,-1]
x = [1,-1, 0, 0]
q = deque([])
for i in range(h):
    for j in range(w):
        if graph[i][j] == "#":
            q.append((i,j,0))
while q:
    c = q.popleft()
    for i in range(4):
        nh = c[0]+y[i]
        nw = c[1]+x[i]
        if nh < 0 or nh >= h or nw < 0 or nw >= w or graph[nh][nw] == "#":continue
        graph[nh][nw] = "#"
        q.append((nh,nw,c[2]+1))
print(c[2])

Fixed submission:
from collections import deque
h, w = map(int,input().split())
graph = []
finished = [[False for _ in range(w)] for _ in range(h)]
y = [0, 0, 1,-1]
x = [1,-1, 0, 0]
q = deque([])
for i in range(h):
    a = input()
    graph.append(a)
    for j in range(w):
        if a[j] == "#":
            q.append((i,j,0))
while q:
    c = q.popleft()
    for i in range(4):
        nh = c[0]+y[i]
        nw = c[1]+x[i]
        if nh < 0 or nh >= h or nw < 0 or nw >= w or graph[nh][nw] == "#" or finished[nh][nw]:continue
        finished[nh][nw] = True
        q.append((nh,nw,c[2]+1))
print(c[2])