Buggy python submission (verdict: Runtime Error):
    from collections import deque
    INF = float("inf")
     
    h, w = map(int, input().split())
    ch, cw = map(int, input().split())
    dh, dw = map(int, input().split())
    ch, cw = ch-1, cw-1
    dh, dw = dh-1, dw-1
    S = [input() for _ in range(h)]
     
    dist = [[INF] * w for _ in range(h)]
    dist[ch][cw] = 0
    q = deque([(cw, ch)])
     
    while q:
        x, y = q.popleft()
        for _x in range(-2, 3):
            for _y in range(-2, 3):
                if _x == _y == 0:
                    continue
                next_x, next_y = x + _x, y + _y
                if not 0 <= next_x < w:
                    continue
                if not 0 <= next_y < h:
                    continue
                if S[next_y][next_x] == "#":
                    continue
                if abs(_x) + abs(_y) <= 1:
                    if dist[next_y][next_x] <= dist[y][x]:
                        continue
                    q.appendleft((next_x, next_y))
                    dist[next_y][next_x] = dist[y][x]
                else:
                    if dist[next_y][next_x] <= dist[y][x] + 1:
                        continue
                    q.append((next_x, next_y))
                    dist[next_y][next_x] = dist[y][x] + 1
     
    if dist[dh][dw] != INF:
        print(dist[dh][dw])
    else:
        print(-1)

Fixed submission:
from collections import deque
INF = float("inf")

h, w = map(int, input().split())
ch, cw = map(int, input().split())
dh, dw = map(int, input().split())
ch, cw = ch-1, cw-1
dh, dw = dh-1, dw-1
S = [input() for _ in range(h)]

dist = [[INF] * w for _ in range(h)]
dist[ch][cw] = 0
q = deque([(cw, ch)])

while q:
    x, y = q.popleft()
    for _x in range(-2, 3):
        for _y in range(-2, 3):
            if _x == _y == 0:
                continue
            next_x, next_y = x + _x, y + _y
            if not 0 <= next_x < w:
                continue
            if not 0 <= next_y < h:
                continue
            if S[next_y][next_x] == "#":
                continue
            if abs(_x) + abs(_y) <= 1:
                if dist[next_y][next_x] <= dist[y][x]:
                    continue
                q.appendleft((next_x, next_y))
                dist[next_y][next_x] = dist[y][x]
            else:
                if dist[next_y][next_x] <= dist[y][x] + 1:
                    continue
                q.append((next_x, next_y))
                dist[next_y][next_x] = dist[y][x] + 1

if dist[dh][dw] != INF:
    print(dist[dh][dw])
else:
    print(-1)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
INF = float("inf")

h, w = map(int, input().split())
ch, cw = map(int, input().split())
dh, dw = map(int, input().split())
ch, cw = ch-1, cw-1
dh, dw = dh-1, dw-1
S = [input() for _ in range(h)]

dist = [[INF] * w for _ in range(h)]
dist[ch][cw] = 0
q = deque([(cw, ch)])

while q:
    x, y = q.popleft()
    for _x in range(-2, 3):
        for _y in range(-2, 3):
            if _x == _y == 0:
                continue
            next_x, next_y = x + _x, y + _y
            if not 0 <= next_x < w:
                continue
            if not 0 <= next_y < h:
                continue
            if S[next_y][next_x] == "#":
                continue
            if abs(_x) + abs(_y) <= 1:
                if dist[next_y][next_x] <= dist[y][x]:
                    continue
                q.appendleft((next_x, next_y))
                dist[next_y][next_x] = dist[y][x]
            else:
                if dist[next_y][next_x] <= dist[y][x] + 1:
                    continue
                q.append((next_x, next_y))
                dist[next_y][next_x] = dist[y][x] + 1

if dist[dh][dw] != INF:
    print(dist[dh][dw])
else:
    print(-1)


Fixed submission:
from collections import deque
INF = float("inf")

h, w = map(int, input().split())
ch, cw = map(int, input().split())
dh, dw = map(int, input().split())
ch, cw = ch-1, cw-1
dh, dw = dh-1, dw-1
S = [input() for _ in range(h)]

dist = [[INF] * w for _ in range(h)]
dist[ch][cw] = 0
q = deque([(cw, ch)])

while q:
    x, y = q.popleft()
    for _x in range(-2, 3):
        for _y in range(-2, 3):
            if _x == _y == 0:
                continue
            next_x, next_y = x + _x, y + _y
            if not 0 <= next_x < w:
                continue
            if not 0 <= next_y < h:
                continue
            if S[next_y][next_x] == "#":
                continue
            if abs(_x) + abs(_y) <= 1:
                if dist[next_y][next_x] <= dist[y][x]:
                    continue
                q.appendleft((next_x, next_y))
                dist[next_y][next_x] = dist[y][x]
            else:
                if dist[next_y][next_x] <= dist[y][x] + 1:
                    continue
                q.append((next_x, next_y))
                dist[next_y][next_x] = dist[y][x] + 1

if dist[dh][dw] != INF:
    print(dist[dh][dw])
else:
    print(-1)