Buggy python submission (verdict: Time Limit Exceeded):
from collections import deque
H, W= map(int, input().split())
CH, CW= map(int, input().split())
DH, DW= map(int, input().split())
S = [list(map(str, input())) for _ in range(H)]
q = deque([(CH-1, CW-1, 0)])
while q:
    h, w, c = q.popleft()
    if S[h][w] == '.':
        S[h][w] = c
        for i in range(-2, 3):
            for j in range(-2, 3):
                if 0<=h+i<H and 0<=w+j<W and S[h+i][w+j] == '.':
                    if abs(i)+abs(j) == 1:
                        q.appendleft((h+i, w+j, c))
                    elif abs(i)+abs(j) >= 2:
                        q.append((h+i, w+j, c+1))
if S[DH-1][DW-1] == '.':
    print(-1)
else:
    print(S[DH-1][DW-1])

Fixed submission:
from collections import deque
H, W= map(int, input().split())
CH, CW= map(int, input().split())
DH, DW= map(int, input().split())
S = [list(map(str, input())) for _ in range(H)]
q = deque([(CH-1, CW-1, 0)])
while q:
    h, w, c = q.popleft()
    if S[h][w] == '.':
        S[h][w] = c
        for i in range(-2, 3):
            for j in range(-2, 3):
                if 0<=h+i<H and 0<=w+j<W and S[h+i][w+j] == '.':
                    if abs(i)+abs(j) == 1:
                        q.appendleft((h+i, w+j, c))
                    elif abs(i)+abs(j) >= 2:
                        q.append((h+i, w+j, c+1))
if S[DH-1][DW-1] == '.':
    print(-1)
else:
    print(S[DH-1][DW-1])

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())
l = [list(input())for i in range(h)]
dist=[[-1 for _ in range(w)] for _ in range(h)]
d=[[1,0],[0,1],[-1,0],[0,-1]]
D=[[1,0],[0,1],[-1,0],[0,-1],[1,1],[-1,1],[-1,1],[-1,-1],[0,2],[2,0],[0,-2],[-2,0],[1,2],[1,-2],[-1,2],[-1,-2],[2,1],[2,-1],[-2,1],[-2,-1],[2,2],[2,-2],[-2,2],[-2,-2]]
M = [-1]
ans = 0

q=deque([[ch-1,cw-1]])
dist[ch-1][cw-1]=0
while q:
    y,x=q.pop()
    for dy,dx in d:
        ny,nx=y+dy,x+dx
        if 0<=ny and ny<h and 0<=nx and nx<w and dist[ny][nx]==-1:
            if l[ny][nx]=='.':
                q.append([ny,nx])
            if l[nx][ny]=='#':
                for Dx,Dy in D:
                    Nx,Ny = y+Dx,y+Dy
                    if 0<=ny and ny<h and 0<=nx and nx<w and dist[ny][nx]==-1:
                        if l[ny][nx]=='.':
                            q.append([Ny,Nx])
                        if l[Ny][Nx]=='#':
                            q.appendleft([ny,nx])
            dist[ny][nx]=dist[y][x]+(l[ny][nx]=='#')
print(dist[dh-1][dw-1])

Fixed submission:
from collections import deque
H, W= map(int, input().split())
CH, CW= map(int, input().split())
DH, DW= map(int, input().split())
S = [list(map(str, input())) for _ in range(H)]
q = deque([(CH-1, CW-1, 0)])
while q:
    h, w, c = q.popleft()
    if S[h][w] == '.':
        S[h][w] = c
        for i in range(-2, 3):
            for j in range(-2, 3):
                if 0<=h+i<H and 0<=w+j<W and S[h+i][w+j] == '.':
                    if abs(i)+abs(j) == 1:
                        q.appendleft((h+i, w+j, c))
                    elif abs(i)+abs(j) >= 2:
                        q.append((h+i, w+j, c+1))
if S[DH-1][DW-1] == '.':
    print(-1)
else:
    print(S[DH-1][DW-1])