Buggy python submission (verdict: Runtime Error):
from collections import deque


def solve():
    H, W = map(int, input().split())
    CH, CW = map(int, input().split())
    DH, DW = map(int, input().split())
    S = ["##"+input()+"##" for _ in range(H)]
    for i in range(2):
        S.insert(0, "#"*(W+4))
        S.append("#"*(W+4))

    inf = int(1e9)
    cost = [[inf for _ in range(W+4)] for _ in range(H+4)]
    cost0 = deque()
    ans = -1

    cost0.append((CH+1, CW+1, 0))
    cost[CH+1][CW+1] = 0

    move = [(1, 0), (0, 1), (-1, 0), (0, -1)]
    warp = [(i, j) for i in range(-2, 3) for j in range(-2, 3) if (i, j) not in [(0, 0)]+move]

    cost1 = deque()

    while cost0:
        h, w, c = cost0.popleft()
        cost1.append((h, w, c))

        for i, j in move:
            dh = h+i
            dw = w+j
            if S[dh][dw] == "." and c < cost[dh][dw]:
                cost[dh][dw] = c
                cost0.appendleft((dh, dw, cost[dh][dw]))

        if len(cost0) == 0:
            while cost1:
                h, w, c = cost1.popleft()
                for i, j in warp:
                    dh = h+i
                    dw = h+j
                    if S[dh][dw] == "." and c+1 < cost[dh][dw]:
                        cost[dh][dw] = c+1
                        cost0.append((dh, dw, cost[dh][dw]))

        if cost[DH+1][DW+1] != inf:
            ans = cost[DH+1][DW+1]

    print(ans)


if __name__ == "__main__":
    solve()


Fixed submission:
from collections import deque


def solve():
    H, W = map(int, input().split())
    CH, CW = map(int, input().split())
    DH, DW = map(int, input().split())
    S = ["##"+input()+"##" for _ in range(H)]
    for i in range(2):
        S.insert(0, "#"*(W+4))
        S.append("#"*(W+4))

    inf = int(1e9)
    cost = [[inf for _ in range(W+4)] for _ in range(H+4)]
    cost0 = deque()
    ans = -1

    cost0.append((CH+1, CW+1, 0))
    cost[CH+1][CW+1] = 0

    move = [(1, 0), (0, 1), (-1, 0), (0, -1)]
    warp = [(i, j) for i in range(-2, 3) for j in range(-2, 3) if (i, j) not in [(0, 0)]+move]

    cost1 = deque()

    while cost0:
        h, w, c = cost0.popleft()
        cost1.append((h, w, c))

        for i, j in move:
            dh = h+i
            dw = w+j
            if S[dh][dw] == "." and c < cost[dh][dw]:
                cost[dh][dw] = c
                cost0.appendleft((dh, dw, cost[dh][dw]))

        if len(cost0) == 0:
            while cost1:
                h, w, c = cost1.popleft()
                for i, j in warp:
                    dh = h+i
                    dw = w+j
                    if S[dh][dw] == "." and c+1 < cost[dh][dw]:
                        cost[dh][dw] = c+1
                        cost0.append((dh, dw, cost[dh][dw]))

        if cost[DH+1][DW+1] != inf:
            ans = cost[DH+1][DW+1]

    print(ans)


if __name__ == "__main__":
    solve()

Buggy python submission (verdict: Runtime Error):
from collections import deque

H, W = map(int, input().split())
CH, CW = map(int, input().split())
DH, DW = map(int, input().split())
S = ["##"+input()+"##" for _ in range(H)]
for i in range(2):
    S.insert(0, "#"*(W+4))
    S.append("#"*(W+4))

inf = int(1e9)
cost = [[inf for _ in range(W+4)] for _ in range(H+4)]
cost0 = deque()
ans = -1

cost0.append((CH+1, CW+1, 0))
cost[CH+1][CW+1] = 0

move = [(1, 0), (0, 1), (-1, 0), (0, -1)]
warp = [(i, j) for i in range(-2, 3) for j in range(-2, 3) if (i, j) not in [(0, 0)]+move]

cost1 = deque()

while cost0:
    h, w, c = cost0.popleft()
    cost1.append((h, w, c))

    for i, j in move:
        dh = h+i
        dw = w+j
        if S[dh][dw] == "." and c < cost[dh][dw]:
            cost[dh][dw] = c
            cost0.appendleft((dh, dw, cost[dh][dw]))

    if len(cost0) == 0:
        while cost1:
            h, w, c = cost1.popleft()
            for i, j in warp:
                dh = h+i
                dw = h+j
                if S[dh][dw] == "." and c+1 < cost[dh][dw]:
                    cost[dh][dw] = c+1
                    cost0.append((dh, dw, cost[dh][dw]))

    if cost[DH+1][DW+1] != inf:
        ans = cost[DH+1][DW+1]

print(ans)


Fixed submission:
from collections import deque


def solve():
    H, W = map(int, input().split())
    CH, CW = map(int, input().split())
    DH, DW = map(int, input().split())
    S = ["##"+input()+"##" for _ in range(H)]
    for i in range(2):
        S.insert(0, "#"*(W+4))
        S.append("#"*(W+4))

    inf = int(1e9)
    cost = [[inf for _ in range(W+4)] for _ in range(H+4)]
    cost0 = deque()
    ans = -1

    cost0.append((CH+1, CW+1, 0))
    cost[CH+1][CW+1] = 0

    move = [(1, 0), (0, 1), (-1, 0), (0, -1)]
    warp = [(i, j) for i in range(-2, 3) for j in range(-2, 3) if (i, j) not in [(0, 0)]+move]

    cost1 = deque()

    while cost0:
        h, w, c = cost0.popleft()
        cost1.append((h, w, c))

        for i, j in move:
            dh = h+i
            dw = w+j
            if S[dh][dw] == "." and c < cost[dh][dw]:
                cost[dh][dw] = c
                cost0.appendleft((dh, dw, cost[dh][dw]))

        if len(cost0) == 0:
            while cost1:
                h, w, c = cost1.popleft()
                for i, j in warp:
                    dh = h+i
                    dw = w+j
                    if S[dh][dw] == "." and c+1 < cost[dh][dw]:
                        cost[dh][dw] = c+1
                        cost0.append((dh, dw, cost[dh][dw]))

        if cost[DH+1][DW+1] != inf:
            ans = cost[DH+1][DW+1]

    print(ans)


if __name__ == "__main__":
    solve()

Buggy python submission (verdict: Runtime Error):
from collections import deque

H, W = map(int, input().split())
C = list(map(int, input().split()))
D = list(map(int, input().split()))
S = ["##"+input()+"##" for _ in range(H)]
for i in range(2):
    S.insert(0, "#"*(W+4))
    S.append("#"*(W+4))

inf = int(1e9)
cost = [[inf for _ in range(W+4)] for _ in range(H+4)]
cost0 = deque()
ans = -1

cost0.append((C[0]+1, C[1]+1, 0))
cost[C[0]+1][C[1]+1] = 0

move = [(1, 0), (0, 1), (-1, 0), (0, -1)]
warp = [(i, j) for i in range(-2, 3) for j in range(-2, 3) if (i, j) not in [(0, 0)]+move]

cost1 = deque()

while cost0:
    h, w, c = cost0.popleft()
    cost1.append((h, w, c))

    for i, j in move:
        dh = h+i
        dw = w+j
        if S[dh][dw] == "." and c < cost[dh][dw]:
            cost[dh][dw] = c
            cost0.appendleft((dh, dw, cost[dh][dw]))

    if len(cost0) == 0:
        while cost1:
            h, w, c = cost1.popleft()
            for i, j in warp:
                dh = h+i
                dw = h+j
                if S[dh][dw] == "." and c+1 < cost[dh][dw]:
                    cost[dh][dw] = c+1
                    cost0.append((dh, dw, cost[dh][dw]))

    if cost[D[0]+1][D[1]+1] != inf:
        ans = cost[D[0]+1][D[1]+1]

print(ans)


Fixed submission:
from collections import deque


def solve():
    H, W = map(int, input().split())
    CH, CW = map(int, input().split())
    DH, DW = map(int, input().split())
    S = ["##"+input()+"##" for _ in range(H)]
    for i in range(2):
        S.insert(0, "#"*(W+4))
        S.append("#"*(W+4))

    inf = int(1e9)
    cost = [[inf for _ in range(W+4)] for _ in range(H+4)]
    cost0 = deque()
    ans = -1

    cost0.append((CH+1, CW+1, 0))
    cost[CH+1][CW+1] = 0

    move = [(1, 0), (0, 1), (-1, 0), (0, -1)]
    warp = [(i, j) for i in range(-2, 3) for j in range(-2, 3) if (i, j) not in [(0, 0)]+move]

    cost1 = deque()

    while cost0:
        h, w, c = cost0.popleft()
        cost1.append((h, w, c))

        for i, j in move:
            dh = h+i
            dw = w+j
            if S[dh][dw] == "." and c < cost[dh][dw]:
                cost[dh][dw] = c
                cost0.appendleft((dh, dw, cost[dh][dw]))

        if len(cost0) == 0:
            while cost1:
                h, w, c = cost1.popleft()
                for i, j in warp:
                    dh = h+i
                    dw = w+j
                    if S[dh][dw] == "." and c+1 < cost[dh][dw]:
                        cost[dh][dw] = c+1
                        cost0.append((dh, dw, cost[dh][dw]))

        if cost[DH+1][DW+1] != inf:
            ans = cost[DH+1][DW+1]

    print(ans)


if __name__ == "__main__":
    solve()

Buggy python submission (verdict: Runtime Error):
from queue import Queue
from collections import deque

H, W = map(int, input().split())
C = list(map(int, input().split()))
D = list(map(int, input().split()))
S = ["##"+input()+"##" for _ in range(H)]
for i in range(2):
    S.insert(0, "#"*(W+4))
    S.append("#"*(W+4))

inf = int(1e9)
cost = [[inf for _ in range(W+4)] for _ in range(H+4)]
cost0 = deque()
ans = -1

cost0.append((C[0]+1, C[1]+1, 0))
cost[C[0]+1][C[1]+1] = 0

move = [(1, 0), (0, 1), (-1, 0), (0, -1)]
warp = [(i, j) for i in range(-2, 3) for j in range(-2, 3) if (i, j) not in [(0, 0)]+move]

cost1 = deque()

while cost0:
    h, w, c = cost0.popleft()
    cost1.append((h, w, c))

    for i, j in move:
        dh = h+i
        dw = w+j
        if S[dh][dw] == "." and c < cost[dh][dw]:
            cost[dh][dw] = c
            cost0.appendleft((dh, dw, cost[dh][dw]))

    while cost1:
        h, w, c = cost1.popleft()
        for i, j in warp:
            dh = h+i
            dw = h+j
            if S[dh][dw] == "." and c+1 < cost[dh][dw]:
                cost[dh][dw] = c+1
                cost0.append((dh, dw, cost[dh][dw]))

    if cost[D[0]+1][D[1]+1] != inf:
        ans = cost[D[0]+1][D[1]+1]

print(ans)


Fixed submission:
from collections import deque


def solve():
    H, W = map(int, input().split())
    CH, CW = map(int, input().split())
    DH, DW = map(int, input().split())
    S = ["##"+input()+"##" for _ in range(H)]
    for i in range(2):
        S.insert(0, "#"*(W+4))
        S.append("#"*(W+4))

    inf = int(1e9)
    cost = [[inf for _ in range(W+4)] for _ in range(H+4)]
    cost0 = deque()
    ans = -1

    cost0.append((CH+1, CW+1, 0))
    cost[CH+1][CW+1] = 0

    move = [(1, 0), (0, 1), (-1, 0), (0, -1)]
    warp = [(i, j) for i in range(-2, 3) for j in range(-2, 3) if (i, j) not in [(0, 0)]+move]

    cost1 = deque()

    while cost0:
        h, w, c = cost0.popleft()
        cost1.append((h, w, c))

        for i, j in move:
            dh = h+i
            dw = w+j
            if S[dh][dw] == "." and c < cost[dh][dw]:
                cost[dh][dw] = c
                cost0.appendleft((dh, dw, cost[dh][dw]))

        if len(cost0) == 0:
            while cost1:
                h, w, c = cost1.popleft()
                for i, j in warp:
                    dh = h+i
                    dw = w+j
                    if S[dh][dw] == "." and c+1 < cost[dh][dw]:
                        cost[dh][dw] = c+1
                        cost0.append((dh, dw, cost[dh][dw]))

        if cost[DH+1][DW+1] != inf:
            ans = cost[DH+1][DW+1]

    print(ans)


if __name__ == "__main__":
    solve()