Buggy python submission (verdict: Time Limit Exceeded):
h,w = list(map(int, input().split()))
# 初期位置
ch,cw = list(map(int, input().split()))
# ゴール位置
dh,dw = list(map(int, input().split()))
b = [['#']*(w+2)]
for _ in range(h):
    b.append(['#'] + list(input()) + ['#'])
b.append(['#']*(w+2))

from collections import deque
q = deque()
nq = deque()
q.append((ch, cw))

visit = [[False]*(w+2) for _ in range(h+2)]

warp = 0
while q or nq:
    while q:
        y,x = q.popleft()
        if (y,x) == (dh,dw):
            print(warp)
            exit()
        if visit[y][x]:
            continue
        visit[y][x] = True
        for dx,dy in ((-1,0),(1,0),(0,-1),(0,1)):
            if b[y+dy][x+dx] == '.':
                if not visit[y+dy][x+dx] and (y+dy, x+dx) not in q:
                    q.append((y+dy, x+dx))
            else:
                for dx in (-2,-1,0,1,2):
                    for dy in (-2,-1,0,1,2):
                        if y+dy > h or x + dx > w:
                            continue
                        if b[y+dy][x+dx] == '.':
                            if not visit[y+dy][x+dx] and (y+dy, x+dx) not in nq:
                                nq.append((y+dy, x+dx))
    q = nq
    nq = deque()
    warp += 1
    
print(-1)

Fixed submission:
h,w = list(map(int, input().split()))
# 初期位置
ch,cw = list(map(int, input().split()))
# ゴール位置
dh,dw = list(map(int, input().split()))
b = [['#']*(w+2)]
for _ in range(h):
    b.append(['#'] + list(input()) + ['#'])
b.append(['#']*(w+2))

from collections import deque
q = deque()
nq = deque()
q.append((ch, cw))

visit = [[False]*(w+2) for _ in range(h+2)]

warp = 0
while q or nq:
    while q:
        y,x = q.popleft()
        if (y,x) == (dh,dw):
            print(warp)
            exit()
        if visit[y][x]:
            continue
        visit[y][x] = True
        for dx,dy in ((-1,0),(1,0),(0,-1),(0,1)):
            if b[y+dy][x+dx] == '.':
                if not visit[y+dy][x+dx]:
                    q.append((y+dy, x+dx))
            else:
                for dx in (-2,-1,0,1,2):
                    for dy in (-2,-1,0,1,2):
                        if y+dy > h or x + dx > w:
                            continue
                        if b[y+dy][x+dx] == '.':
                            if not visit[y+dy][x+dx]:
                                nq.append((y+dy, x+dx))
    q = nq
    nq = deque()
    warp += 1
    
print(-1)

Buggy python submission (verdict: Time Limit Exceeded):
h,w = list(map(int, input().split()))
# 初期位置
ch,cw = list(map(int, input().split()))
# ゴール位置
dh,dw = list(map(int, input().split()))
b = [['#']*(w+2)]
for _ in range(h):
    b.append(['#'] + list(input()) + ['#'])
b.append(['#']*(w+2))

from collections import deque
q = deque()
nq = deque()
q.append((ch, cw))

visit = [[False]*(w+2) for _ in range(h+2)]

warp = 0
while q or nq:
    while q:
        y,x = q.popleft()
        if (y,x) == (dh,dw):
            print(warp)
            exit()
        if visit[y][x]:
            continue
        visit[y][x] = True
        for dx,dy in ((-1,0),(1,0),(0,-1),(0,1)):
            if b[y+dy][x+dx] == '.':
                if not visit[y+dy][x+dx] and (y+dy, x+dx) not in q:
                    q.append((y+dy, x+dx))
            else:
                for dx in (-2,-1,0,1,2):
                    for dy in (-2,-1,0,1,2):
                        if y+dy > h or x + dx > w:
                            continue
                        if b[y+dy][x+dx] == '.':
                            if not visit[y+dy][x+dx] and (y+dy, x+dx) not in nq:
                                nq.append((y+dy, x+dx))
    q = nq
    nq = deque()
    warp += 1
    
print(-1)

Fixed submission:
h,w = list(map(int, input().split()))
# 初期位置
ch,cw = list(map(int, input().split()))
# ゴール位置
dh,dw = list(map(int, input().split()))
b = [['#']*(w+2)]
for _ in range(h):
    b.append(['#'] + list(input()) + ['#'])
b.append(['#']*(w+2))

from collections import deque
q = deque()
nq = deque()
q.append((ch, cw))

visit = [[False]*(w+2) for _ in range(h+2)]

warp = 0
while q or nq:
    while q:
        y,x = q.popleft()
        if (y,x) == (dh,dw):
            print(warp)
            exit()
        if visit[y][x]:
            continue
        visit[y][x] = True
        for dx,dy in ((-1,0),(1,0),(0,-1),(0,1)):
            if b[y+dy][x+dx] == '.':
                if not visit[y+dy][x+dx]:
                    q.append((y+dy, x+dx))
            else:
                for dx in (-2,-1,0,1,2):
                    for dy in (-2,-1,0,1,2):
                        if y+dy > h or x + dx > w:
                            continue
                        if b[y+dy][x+dx] == '.':
                            if not visit[y+dy][x+dx]:
                                nq.append((y+dy, x+dx))
    q = nq
    nq = deque()
    warp += 1
    
print(-1)