Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
h,w = map(int,input().split())
C = list(map(int,input().split()))
D = list(map(int,input().split()))
S = [[s for s in input()]for _ in range(h)]
que = deque([[C[0]-1,C[1]-1]])
que2 = deque([])
dd = [-1,1]
d1 = [-2,-1,0,1,2]
reach = [[False for _ in range(w)]for _ in range(h)]
reach[C[0]-1][C[1]-1]=True
ans = 0
while que:
    u = que.popleft()
    x,y = u
    if y < 0 or x < 0 or y >= w or x >= h:
        continue
    if S[x][y] == '#':
        continue
    else:
        reach[x][y] = True
    for d in dd:
        xx = x+d
        yy = y+d
        if 0 <= xx < h:
            if S[xx][y] == '.':
                if not reach[xx][y]:
                    que.append([xx,y])
                    reach[xx][y] = True
            else:
                for i in d1:
                    for j in d1:
                        s,t = x+i,y+j
                        if 0<=s<h and 0<=t<w:
                            if S[s][t] == '.' and not reach[s][t]:
                                que2.append([s,t])  
        if 0 <= yy < w:
            if S[x][yy] =='.':
                if not reach[x][yy]:
                    que.append([x,yy])
                    reach[x][yy] = True
            else:
                for i in d1:
                    for j in d1:
                        s,t = x+i,y+j
                        if 0<=s<h and 0<=t<w:
                            if S[s][t] == '.' and not reach[s][t]:
                                que2.append([s,t])  
    if reach[D[0]-1][D[1]-1]:
        print(ans)
        exit()    
    if not que:
        que = que2
        que2 = deque([])
        ans += 1
print(-1)


Fixed submission:
from collections import deque
h,w = map(int,input().split())
C = list(map(int,input().split()))
D = list(map(int,input().split()))
S = [[s for s in input()]for _ in range(h)]
que = deque([[C[0]-1,C[1]-1]])
que2 = deque([])
dd = [-1,1]
d1 = [-2,-1,0,1,2]
reach = [[False for _ in range(w)]for _ in range(h)]
added = [[False for _ in range(w)]for _ in range(h)]
reach[C[0]-1][C[1]-1]=True
added[C[0]-1][C[1]-1]=True
ans = 0
while que:
    u = que.popleft()
    x,y = u
    if not reach[x][y]:
        reach[x][y] = True
    for d in dd:
        xx = x+d
        yy = y+d
        if 0 <= xx < h:
            if S[xx][y] == '.':
                if not reach[xx][y]:
                    que.append([xx,y])
                    reach[xx][y] = True
                    added[xx][y] = True

        if 0 <= yy < w:
            if S[x][yy] =='.':
                if not reach[x][yy]:
                    que.append([x,yy])
                    reach[x][yy] = True
                    added[x][yy] = True 
    for i in d1:
        for j in d1:
            s,t = x+i,y+j
            if 0<=s<h and 0<=t<w:
                if S[s][t] == '.' and not added[s][t]:
                    que2.append([s,t]) 
                    added[s][t] = True

    if reach[D[0]-1][D[1]-1]:
        print(ans)
        exit()    
    if not que:
        que = que2
        que2 = deque([])
        ans += 1
print(-1)

Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
h,w = map(int,input().split())
C = list(map(int,input().split()))
D = list(map(int,input().split()))
S = [[s for s in input()]for _ in range(h)]
que = deque([[C[0]-1,C[1]-1]])
que2 = deque([])
dd = [-1,1]
d1 = [-2,-1,0,1,2]
reach = [[False for _ in range(w)]for _ in range(h)]
reach[C[0]-1][C[1]-1]=True
ans = 0
while que:
    u = que.popleft()
    x,y = u
    if y < 0 or x < 0 or y >= w or x >= h:
        continue
    if S[x][y] == '#':
        continue
    else:
        reach[x][y] = True
    for d in dd:
        xx = x+d
        yy = y+d
        if 0 <= xx < h:
            if S[xx][y] == '.':
                if not reach[xx][y]:
                    que.append([xx,y])
                    reach[xx][y] = True
            else:
                for i in d1:
                    for j in d1:
                        s,t = x+i,y+j
                        if 0<=s<h and 0<=t<w:
                            if S[s][t] == '.' and not reach[s][t]:
                                que2.append([s,t])  
        if 0 <= yy < w:
            if S[x][yy] =='.':
                if not reach[x][yy]:
                    que.append([x,yy])
                    reach[x][yy] = True
            else:
                for i in d1:
                    for j in d1:
                        s,t = x+i,y+j
                        if 0<=s<h and 0<=t<w:
                            if S[s][t] == '.' and not reach[s][t]:
                                que2.append([s,t])  
    if reach[D[0]-1][D[1]-1]:
        print(ans)
        exit()    
    if not que:
        que = que2
        que2 = deque([])
        ans += 1
print(-1)


Fixed submission:
from collections import deque
h,w = map(int,input().split())
C = list(map(int,input().split()))
D = list(map(int,input().split()))
S = [[s for s in input()]for _ in range(h)]
que = deque([[C[0]-1,C[1]-1]])
que2 = deque([])
dd = [-1,1]
d1 = [-2,-1,0,1,2]
reach = [[False for _ in range(w)]for _ in range(h)]
added = [[False for _ in range(w)]for _ in range(h)]
reach[C[0]-1][C[1]-1]=True
added[C[0]-1][C[1]-1]=True
ans = 0
while que:
    u = que.popleft()
    x,y = u
    if not reach[x][y]:
        reach[x][y] = True
    for d in dd:
        xx = x+d
        yy = y+d
        if 0 <= xx < h:
            if S[xx][y] == '.':
                if not reach[xx][y]:
                    que.append([xx,y])
                    reach[xx][y] = True
                    added[xx][y] = True

        if 0 <= yy < w:
            if S[x][yy] =='.':
                if not reach[x][yy]:
                    que.append([x,yy])
                    reach[x][yy] = True
                    added[x][yy] = True 
    for i in d1:
        for j in d1:
            s,t = x+i,y+j
            if 0<=s<h and 0<=t<w:
                if S[s][t] == '.' and not added[s][t]:
                    que2.append([s,t]) 
                    added[s][t] = True

    if reach[D[0]-1][D[1]-1]:
        print(ans)
        exit()    
    if not que:
        que = que2
        que2 = deque([])
        ans += 1
print(-1)