Buggy python submission (verdict: Runtime Error):
import collections
H, W = map(int, input().split())
S = [input() for _ in range(H)]
def f():
    q = collections.deque()
    dist = [[float("inf")] * W for _ in range(H)]
    for i in range(H):
        for k in range(W):
            if S[i][k] == '#':
                q.append((i,k))
                dist[i][k] = 0
    dx = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    while len(q) != 0:
        h, w = q.popleft()
        d = dist[h][w]
        for x, y in dx:
            h2 = h + y
            w2 = w + x
            if h2 >= 0 and h2 < W and w2 >= 0 and w2 < H:
                if dist[h2][w2] == float("inf"):
                    dist[h2][w2] = d+1
                    q.append((h2, w2))
    return dist
ans = 0
dist = f()
for i in range(H):
    for k in range(W):
        ans = max(ans,dist[i][k])
print(ans)

Fixed submission:
import collections
H, W = map(int, input().split())
S = [input() for _ in range(H)]
def f():
    q = collections.deque()
    dist = [[float("inf")] * W for _ in range(H)]
    for i in range(H):
        for k in range(W):
            if S[i][k] == '#':
                q.append((i,k))
                dist[i][k] = 0
    dx = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    while len(q) != 0:
        h, w = q.popleft()
        d = dist[h][w]
        for x, y in dx:
            h2 = h + y
            w2 = w + x
            if h2 >= 0 and h2 < H and w2 >= 0 and w2 < W:
                if dist[h2][w2] == float("inf"):
                    dist[h2][w2] = d+1
                    q.append((h2, w2))
    return dist
ans = 0
dist = f()
for i in range(H):
    for k in range(W):
        ans = max(ans,dist[i][k])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import collections
H, W = map(int, input().split())
S = [input() for _ in range(H)]
def f(sx, sy):
    q = collections.deque()
    q.append((sx, sy))
    dist = [[float("inf") for w in range(W)] for h in range(H)]
    dist[sx][sy] = 0
    dx = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    while len(q) != 0:
        h, w = q.popleft()
        d = dist[h][w]
        for x, y in dx:
            h2 = h + y
            w2 = w + x
            if h2 >= 0 and h2 < W and w2 >= 0 and w2 < H:
                if S[h2][w2] == "." and dist[h2][w2] == float("inf"):
                    dist[h2][w2] = d+1
                    q.append((h2, w2))
                if S[h2][w2] == '#':
                    return d + 1
    return 0
ans = 0
for i in range(H):
    for k in range(W):
        if S[i][k] == '.':
            ans = max(ans,f(k,i))
print(ans)

Fixed submission:
import collections
H, W = map(int, input().split())
S = [input() for _ in range(H)]
def f():
    q = collections.deque()
    dist = [[float("inf")] * W for _ in range(H)]
    for i in range(H):
        for k in range(W):
            if S[i][k] == '#':
                q.append((i,k))
                dist[i][k] = 0
    dx = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    while len(q) != 0:
        h, w = q.popleft()
        d = dist[h][w]
        for x, y in dx:
            h2 = h + y
            w2 = w + x
            if h2 >= 0 and h2 < H and w2 >= 0 and w2 < W:
                if dist[h2][w2] == float("inf"):
                    dist[h2][w2] = d+1
                    q.append((h2, w2))
    return dist
ans = 0
dist = f()
for i in range(H):
    for k in range(W):
        ans = max(ans,dist[i][k])
print(ans)

Buggy python submission (verdict: Time Limit Exceeded):
import collections
H, W = map(int, input().split())
S = [input() for _ in range(H)]
def f(sx, sy):
    q = collections.deque()
    q.append((sx, sy))
    dist = [[float("inf") for w in range(W)] for h in range(H)]
    dist[sx][sy] = 0
    dx = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    while len(q) != 0:
        h, w = q.popleft()
        d = dist[h][w]
        for x, y in dx:
            h2 = h + y
            w2 = w + x
            if h2 >= 0 and h2 < W and w2 >= 0 and w2 < H:
                if S[h2][w2] == "." and dist[h2][w2] == float("inf"):
                    dist[h2][w2] = d+1
                    q.append((h2, w2))
                if S[h2][w2] == '#':
                    return d + 1
    return 0
ans = 0
for i in range(H):
    for k in range(W):
        if S[i][k] == '.':
            ans = max(ans,f(k,i))
print(ans)

Fixed submission:
import collections
H, W = map(int, input().split())
S = [input() for _ in range(H)]
def f():
    q = collections.deque()
    dist = [[float("inf")] * W for _ in range(H)]
    for i in range(H):
        for k in range(W):
            if S[i][k] == '#':
                q.append((i,k))
                dist[i][k] = 0
    dx = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    while len(q) != 0:
        h, w = q.popleft()
        d = dist[h][w]
        for x, y in dx:
            h2 = h + y
            w2 = w + x
            if h2 >= 0 and h2 < H and w2 >= 0 and w2 < W:
                if dist[h2][w2] == float("inf"):
                    dist[h2][w2] = d+1
                    q.append((h2, w2))
    return dist
ans = 0
dist = f()
for i in range(H):
    for k in range(W):
        ans = max(ans,dist[i][k])
print(ans)

Buggy python submission (verdict: Runtime Error):
import collections
H, W = map(int, input().split())
S = [input() for _ in range(H)]
brack_point = []
for i in range(H):
    for k in range(W):
        if S[i][k] == '#':
            brack_point.append([i,k])
def f(sx, sy, gx, gy):
    q = collections.deque()
    q.append((sx, sy))
    dist = [[float("inf") for w in range(H)] for h in range(W)]
    dist[sx][sy] = 0
    dx = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    while len(q) != 0:
        h, w = q.popleft()
        d = dist[h][w]
        for x, y in dx:
            h2 = h + y
            w2 = w + x
            if h2 >= 0 and h2 < W and w2 >= 0 and w2 < H:
                if S[h2][w2] == "." and dist[h2][w2] == float("inf"):
                    dist[h2][w2] = d+1
                    q.append((h2, w2))
    return dist[gy][gx]
ans = 0
for i in range(H):
    for k in range(W):
        if S[i][k] == '.':
            tmp = float('inf')
            for point in brack_point:
                tmp = min(tmp,f(point[1],point[0],k,i))
            ans = max(ans,tmp)
print(ans)

Fixed submission:
import collections
H, W = map(int, input().split())
S = [input() for _ in range(H)]
def f():
    q = collections.deque()
    dist = [[float("inf")] * W for _ in range(H)]
    for i in range(H):
        for k in range(W):
            if S[i][k] == '#':
                q.append((i,k))
                dist[i][k] = 0
    dx = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    while len(q) != 0:
        h, w = q.popleft()
        d = dist[h][w]
        for x, y in dx:
            h2 = h + y
            w2 = w + x
            if h2 >= 0 and h2 < H and w2 >= 0 and w2 < W:
                if dist[h2][w2] == float("inf"):
                    dist[h2][w2] = d+1
                    q.append((h2, w2))
    return dist
ans = 0
dist = f()
for i in range(H):
    for k in range(W):
        ans = max(ans,dist[i][k])
print(ans)

Buggy python submission (verdict: Runtime Error):
import collections
H, W = map(int, input().split())
S = [input() for _ in range(H)]
brack_point = []
for i in range(H):
    for k in range(W):
        if S[i][k] == '#':
            brack_point.append([i,k])
def f(sx, sy, gx, gy):
    q = collections.deque()
    q.append((sx, sy))
    dist = [[float("inf") for w in range(H)] for h in range(W)]
    dist[sx][sy] = 0
    dx = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    while len(q) != 0:
        h, w = q.popleft()
        d = dist[h][w]
        for x, y in dx:
            h2 = h + y
            w2 = w + x
            if h2 >= 0 and h2 < W and w2 >= 0 and w2 < H:
                if S[h2][w2] == "." and dist[h2][w2] == float("inf"):
                    dist[h2][w2] = d+1
                    q.append((h2, w2))
    return dist[gy][gx]
ans = 0
for i in range(H):
    for k in range(W):
        if S[i][k] == '.':
            tmp = float('inf')
            for point in brack_point:
                tmp = min(tmp,f(point[0],point[1],i,k))
            ans = max(ans,tmp)
print(ans)

Fixed submission:
import collections
H, W = map(int, input().split())
S = [input() for _ in range(H)]
def f():
    q = collections.deque()
    dist = [[float("inf")] * W for _ in range(H)]
    for i in range(H):
        for k in range(W):
            if S[i][k] == '#':
                q.append((i,k))
                dist[i][k] = 0
    dx = [(-1, 0), (1, 0), (0, -1), (0, 1)]
    while len(q) != 0:
        h, w = q.popleft()
        d = dist[h][w]
        for x, y in dx:
            h2 = h + y
            w2 = w + x
            if h2 >= 0 and h2 < H and w2 >= 0 and w2 < W:
                if dist[h2][w2] == float("inf"):
                    dist[h2][w2] = d+1
                    q.append((h2, w2))
    return dist
ans = 0
dist = f()
for i in range(H):
    for k in range(W):
        ans = max(ans,dist[i][k])
print(ans)