Buggy python submission (verdict: Time Limit Exceeded):
from sys import stdin
from collections import deque
input = stdin.readline

H, W = map(int, input().split())
ch, cw = map(int, input().split())
dh, dw = map(int, input().split())
S = [list(input().rstrip()) for _ in range(H)]

dir_h = [0, 0, 1, -1]
dir_w = [1, -1, 0, 0]

seen = [[-1 for _ in range(W)] for _ in range(H)]
edge = []
nex = [[ch - 1, cw - 1]]
num = 0


def bfs():
    q = deque([])

    for h, w in nex:
        q.append([h, w])
        seen[h][w] = num
        while q:
            h, w = q.popleft()

            for dh, dw in zip(dir_h, dir_w):
                nh, nw = h + dh, w + dw

                if nh < 0 or nh >= H or nw < 0 or nw >= W:
                    continue
                elif S[nh][nw] == "#":
                    edge.append([h, w])
                    continue
                elif seen[nh][nw] != -1:
                    continue
                else:
                    seen[nh][nw] = num
                    q.append([nh, nw])


def dfs():
    d = deque([])
    for h, w in edge:
        d.append([h, w])

        while d:
            h, w = d.pop()
            num = seen[h][w]
            for dh in range(-2, 3):
                for dw in range(-2, 3):
                    nh, nw = h + dh, w + dw

                    if nh < 0 or nh >= H or nw < 0 or nw >= W:
                        continue
                    elif S[nh][nw] == "#":
                        continue
                    elif seen[nh][nw] != -1:
                        continue
                    else:
                        seen[nh][nw] = min(num, seen[nh][nw])
                        nex.append([nh, nw])


while True:
    bfs()
    if not edge:
        break
    nex = []
    num += 1
    dfs()
    if not nex:
        break
    edge = []

# for s in seen:
#     print(s)

print(seen[dh - 1][dw - 1])


Fixed submission:
from sys import stdin
from collections import deque
input = stdin.readline

H, W = map(int, input().split())
ch, cw = map(int, input().split())
dh, dw = map(int, input().split())
S = [list(input().rstrip()) for _ in range(H)]

dir_h = [0, 0, 1, -1]
dir_w = [1, -1, 0, 0]

seen = [[-1 for _ in range(W)] for _ in range(H)]
edge = []
nex = [[ch - 1, cw - 1]]
num = 0
group = [[-1 for _ in range(W)] for _ in range(H)]


def bfs():
    q = deque([])

    for h, w in nex:
        if seen[h][w] != -1:
            continue
        q.append([h, w])
        seen[h][w] = num
        while q:
            h, w = q.popleft()

            for dh, dw in zip(dir_h, dir_w):
                nh, nw = h + dh, w + dw

                if nh < 0 or nh >= H or nw < 0 or nw >= W:
                    continue
                elif S[nh][nw] == "#":
                    edge.append([h, w])
                    continue
                elif seen[nh][nw] != -1:
                    continue
                else:
                    seen[nh][nw] = num
                    q.append([nh, nw])


def dfs():
    d = deque([])
    for h, w in edge:
        d.append([h, w])

        while d:
            h, w = d.pop()
            for dh in range(-2, 3):
                for dw in range(-2, 3):
                    nh, nw = h + dh, w + dw

                    if nh < 0 or nh >= H or nw < 0 or nw >= W:
                        continue
                    elif S[nh][nw] == "#":
                        continue
                    elif seen[nh][nw] != -1:
                        continue
                    else:
                        nex.append([nh, nw])


while True:
    bfs()
    if not edge:
        break
    nex = []
    num += 1
    dfs()
    if not nex:
        break
    edge = []

# for s in seen:
#     print(s)

print(seen[dh - 1][dw - 1])

Buggy python submission (verdict: Time Limit Exceeded):
from sys import stdin
from collections import deque
input = stdin.readline

H, W = map(int, input().split())
ch, cw = map(int, input().split())
dh, dw = map(int, input().split())
S = [list(input().rstrip()) for _ in range(H)]

dir_h = [0, 0, 1, -1]
dir_w = [1, -1, 0, 0]

seen = [[-1 for _ in range(W)] for _ in range(H)]
edge = []
nex = [[ch - 1, cw - 1]]
num = 0


def bfs():
    q = deque([])

    for h, w in nex:
        q.append([h, w])
        seen[h][w] = num
        while q:
            h, w = q.popleft()

            for dh, dw in zip(dir_h, dir_w):
                nh, nw = h + dh, w + dw

                if nh < 0 or nh >= H or nw < 0 or nw >= W:
                    continue
                elif S[nh][nw] == "#":
                    edge.append([h, w])
                    continue
                elif seen[nh][nw] != -1:
                    continue
                else:
                    seen[nh][nw] = num
                    q.append([nh, nw])


def dfs():
    d = deque([])
    for h, w in edge:
        d.append([h, w])

        while d:
            h, w = d.pop()
            num = seen[h][w]
            for dh in range(-2, 3):
                for dw in range(-2, 3):
                    nh, nw = h + dh, w + dw

                    if nh < 0 or nh >= H or nw < 0 or nw >= W:
                        continue
                    elif S[nh][nw] == "#":
                        continue
                    elif seen[nh][nw] != -1:
                        continue
                    else:
                        seen[nh][nw] = min(num, seen[nh][nw])
                        nex.append([nh, nw])


while True:
    bfs()
    if not edge:
        break
    nex = []
    num += 1
    dfs()
    if not nex:
        break
    edge = []

# for s in seen:
#     print(s)

print(seen[dh - 1][dw - 1])


Fixed submission:
from sys import stdin
from collections import deque
input = stdin.readline

H, W = map(int, input().split())
ch, cw = map(int, input().split())
dh, dw = map(int, input().split())
S = [list(input().rstrip()) for _ in range(H)]

dir_h = [0, 0, 1, -1]
dir_w = [1, -1, 0, 0]

seen = [[-1 for _ in range(W)] for _ in range(H)]
edge = []
nex = [[ch - 1, cw - 1]]
num = 0
group = [[-1 for _ in range(W)] for _ in range(H)]


def bfs():
    q = deque([])

    for h, w in nex:
        if seen[h][w] != -1:
            continue
        q.append([h, w])
        seen[h][w] = num
        while q:
            h, w = q.popleft()

            for dh, dw in zip(dir_h, dir_w):
                nh, nw = h + dh, w + dw

                if nh < 0 or nh >= H or nw < 0 or nw >= W:
                    continue
                elif S[nh][nw] == "#":
                    edge.append([h, w])
                    continue
                elif seen[nh][nw] != -1:
                    continue
                else:
                    seen[nh][nw] = num
                    q.append([nh, nw])


def dfs():
    d = deque([])
    for h, w in edge:
        d.append([h, w])

        while d:
            h, w = d.pop()
            for dh in range(-2, 3):
                for dw in range(-2, 3):
                    nh, nw = h + dh, w + dw

                    if nh < 0 or nh >= H or nw < 0 or nw >= W:
                        continue
                    elif S[nh][nw] == "#":
                        continue
                    elif seen[nh][nw] != -1:
                        continue
                    else:
                        nex.append([nh, nw])


while True:
    bfs()
    if not edge:
        break
    nex = []
    num += 1
    dfs()
    if not nex:
        break
    edge = []

# for s in seen:
#     print(s)

print(seen[dh - 1][dw - 1])

Buggy python submission (verdict: Time Limit Exceeded):
from sys import stdin
from collections import deque
input = stdin.readline

H, W = map(int, input().split())
ch, cw = map(int, input().split())
dh, dw = map(int, input().split())
S = [list(input().rstrip()) for _ in range(H)]

dir_h = [0, 0, 1, -1]
dir_w = [1, -1, 0, 0]

seen = [[-1 for _ in range(W)] for _ in range(H)]
edge = []
nex = [[ch - 1, cw - 1]]
num = 0


def bfs():
    q = deque([])

    for h, w in nex:
        q.append([h, w])
        seen[h][w] = num
        while q:
            h, w = q.popleft()

            for dh, dw in zip(dir_h, dir_w):
                nh, nw = h + dh, w + dw

                if nh < 0 or nh >= H or nw < 0 or nw >= W:
                    continue
                elif S[nh][nw] == "#":
                    edge.append([h, w])
                    continue
                elif seen[nh][nw] != -1:
                    continue
                else:
                    seen[nh][nw] = num
                    q.append([nh, nw])


def dfs():
    d = deque([])
    for h, w in edge:
        d.append([h, w])

        while d:
            h, w = d.pop()
            num = seen[h][w]
            for dh in range(-2, 3):
                for dw in range(-2, 3):
                    nh, nw = h + dh, w + dw

                    if nh < 0 or nh >= H or nw < 0 or nw >= W:
                        continue
                    elif S[nh][nw] == "#":
                        continue
                    elif seen[nh][nw] != -1:
                        continue
                    else:
                        seen[nh][nw] = min(num, seen[nh][nw])
                        nex.append([nh, nw])


while True:
    bfs()
    nex = []
    num += 1
    dfs()
    if not edge:
        break
    edge = []

# for s in seen:
#     print(s)

print(seen[dh - 1][dw - 1])


Fixed submission:
from sys import stdin
from collections import deque
input = stdin.readline

H, W = map(int, input().split())
ch, cw = map(int, input().split())
dh, dw = map(int, input().split())
S = [list(input().rstrip()) for _ in range(H)]

dir_h = [0, 0, 1, -1]
dir_w = [1, -1, 0, 0]

seen = [[-1 for _ in range(W)] for _ in range(H)]
edge = []
nex = [[ch - 1, cw - 1]]
num = 0
group = [[-1 for _ in range(W)] for _ in range(H)]


def bfs():
    q = deque([])

    for h, w in nex:
        if seen[h][w] != -1:
            continue
        q.append([h, w])
        seen[h][w] = num
        while q:
            h, w = q.popleft()

            for dh, dw in zip(dir_h, dir_w):
                nh, nw = h + dh, w + dw

                if nh < 0 or nh >= H or nw < 0 or nw >= W:
                    continue
                elif S[nh][nw] == "#":
                    edge.append([h, w])
                    continue
                elif seen[nh][nw] != -1:
                    continue
                else:
                    seen[nh][nw] = num
                    q.append([nh, nw])


def dfs():
    d = deque([])
    for h, w in edge:
        d.append([h, w])

        while d:
            h, w = d.pop()
            for dh in range(-2, 3):
                for dw in range(-2, 3):
                    nh, nw = h + dh, w + dw

                    if nh < 0 or nh >= H or nw < 0 or nw >= W:
                        continue
                    elif S[nh][nw] == "#":
                        continue
                    elif seen[nh][nw] != -1:
                        continue
                    else:
                        nex.append([nh, nw])


while True:
    bfs()
    if not edge:
        break
    nex = []
    num += 1
    dfs()
    if not nex:
        break
    edge = []

# for s in seen:
#     print(s)

print(seen[dh - 1][dw - 1])