Buggy python submission (verdict: Time Limit Exceeded):
h,w=map(int,input().split())
Ch,Cw=map(int,input().split())
Dh,Dw=map(int,input().split())
s=[list(input()) for _ in range(h)]

Ch,Cw=Ch-1,Cw-1
Dh,Dw=Dh-1,Dw-1
from heapq import heappop,heappush
todo=[[0,Ch,Cw]]
d=[[-1]*w for _ in range(h)]
d[Ch][Cw]=0
toho=[[0,1],[0,-1],[1,0],[-1,0]]
wiz=[[2,2],[2,1],[2,0],[2,-1],[2,-2],[1,2],[1,1],[1,-1],[1,-2],[0,2],[0,-2],[-1,2],[-1,1],[-1,-1],[-1,-2],[-2,2],[-2,1],[-2,0],[-2,-1],[-2,-2]]
while todo:
  cnt,nh,nw=heappop(todo)
  if d[nh][nw]<cnt:continue
  if [nh,nw]==[Dh,Dw]:
    print(cnt)
    exit()
  for dh,dw in toho:
    if 0<=nh+dh<h and 0<=nw+dw<w and s[nh+dh][nw+dw]!='#':
      if d[nh+dh][nw+dw]==-1 or d[nh+dh][nw+dw]>cnt:
        d[nh+dh][nw+dw]=cnt
        heappush(todo,[cnt,nh+dh,nw+dw])
  for dh,dw in wiz:
    if 0<=nh+dh<h and 0<=nw+dw<w and s[nh+dh][nw+dw]!='#':
      if d[nh+dh][nw+dw]==-1 or d[nh+dh][nw+dw]>cnt+1:
        d[nh+dh][nw+dw]=cnt+1
        heappush(todo,[cnt+1,nh+dh,nw+dw])
print(d[Dh][Dw])


Fixed submission:
h,w=map(int,input().split())
Ch,Cw=map(int,input().split())
Dh,Dw=map(int,input().split())
s=[list(input()) for _ in range(h)]

Ch,Cw=Ch-1,Cw-1
Dh,Dw=Dh-1,Dw-1
todo=[[0,Ch,Cw]]
ntodo=[]
d=[[-1]*w for _ in range(h)]
d[Ch][Cw]=0
toho=[[0,1],[0,-1],[1,0],[-1,0]]
wiz=[[2,2],[2,1],[2,0],[2,-1],[2,-2],[1,2],[1,1],[1,-1],[1,-2],[0,2],[0,-2],[-1,2],[-1,1],[-1,-1],[-1,-2],[-2,2],[-2,1],[-2,0],[-2,-1],[-2,-2]]
while todo or ntodo:
  if not todo:
    todo=ntodo
    ntodo=[]
  cnt,nh,nw=todo.pop()
  if d[nh][nw]<cnt:continue
  for dh,dw in toho:
    if 0<=nh+dh<h and 0<=nw+dw<w and s[nh+dh][nw+dw]!='#':
      if d[nh+dh][nw+dw]==-1 or d[nh+dh][nw+dw]>cnt:
        d[nh+dh][nw+dw]=cnt
        todo.append([cnt,nh+dh,nw+dw])
  for dh,dw in wiz:
    if 0<=nh+dh<h and 0<=nw+dw<w and s[nh+dh][nw+dw]!='#':
      if d[nh+dh][nw+dw]==-1 or d[nh+dh][nw+dw]>cnt+1:
        d[nh+dh][nw+dw]=cnt+1
        ntodo.append([cnt+1,nh+dh,nw+dw])
print(d[Dh][Dw])

Buggy python submission (verdict: Time Limit Exceeded):
h,w=map(int,input().split())
Ch,Cw=map(int,input().split())
Dh,Dw=map(int,input().split())
s=[list(input()) for _ in range(h)]

Ch,Cw=Ch-1,Cw-1
Dh,Dw=Dh-1,Dw-1
todo=[[0,Ch,Cw]]
d=[[-1]*w for _ in range(h)]
d[Ch][Cw]=0
toho=[[0,1],[0,-1],[1,0],[-1,0]]
wiz=[[2,2],[2,1],[2,0],[2,-1],[2,-2],[1,2],[1,1],[1,-1],[1,-2],[0,2],[0,-2],[-1,2],[-1,1],[-1,-1],[-1,-2],[-2,2],[-2,1],[-2,0],[-2,-1],[-2,-2]]
while todo:
  cnt,nh,nw=todo.pop()
  if d[nh][nw]<cnt:continue
  for dh,dw in toho:
    if 0<=nh+dh<h and 0<=nw+dw<w and s[nh+dh][nw+dw]!='#':
      if d[nh+dh][nw+dw]==-1 or d[nh+dh][nw+dw]>cnt:
        d[nh+dh][nw+dw]=cnt
        todo.append([cnt,nh+dh,nw+dw])
  for dh,dw in wiz:
    if 0<=nh+dh<h and 0<=nw+dw<w and s[nh+dh][nw+dw]!='#':
      if d[nh+dh][nw+dw]==-1 or d[nh+dh][nw+dw]>cnt+1:
        d[nh+dh][nw+dw]=cnt+1
        todo.append([cnt+1,nh+dh,nw+dw])
print(d[Dh][Dw])


Fixed submission:
h,w=map(int,input().split())
Ch,Cw=map(int,input().split())
Dh,Dw=map(int,input().split())
s=[list(input()) for _ in range(h)]

Ch,Cw=Ch-1,Cw-1
Dh,Dw=Dh-1,Dw-1
todo=[[0,Ch,Cw]]
ntodo=[]
d=[[-1]*w for _ in range(h)]
d[Ch][Cw]=0
toho=[[0,1],[0,-1],[1,0],[-1,0]]
wiz=[[2,2],[2,1],[2,0],[2,-1],[2,-2],[1,2],[1,1],[1,-1],[1,-2],[0,2],[0,-2],[-1,2],[-1,1],[-1,-1],[-1,-2],[-2,2],[-2,1],[-2,0],[-2,-1],[-2,-2]]
while todo or ntodo:
  if not todo:
    todo=ntodo
    ntodo=[]
  cnt,nh,nw=todo.pop()
  if d[nh][nw]<cnt:continue
  for dh,dw in toho:
    if 0<=nh+dh<h and 0<=nw+dw<w and s[nh+dh][nw+dw]!='#':
      if d[nh+dh][nw+dw]==-1 or d[nh+dh][nw+dw]>cnt:
        d[nh+dh][nw+dw]=cnt
        todo.append([cnt,nh+dh,nw+dw])
  for dh,dw in wiz:
    if 0<=nh+dh<h and 0<=nw+dw<w and s[nh+dh][nw+dw]!='#':
      if d[nh+dh][nw+dw]==-1 or d[nh+dh][nw+dw]>cnt+1:
        d[nh+dh][nw+dw]=cnt+1
        ntodo.append([cnt+1,nh+dh,nw+dw])
print(d[Dh][Dw])

Buggy python submission (verdict: Time Limit Exceeded):
h,w=map(int,input().split())
Ch,Cw=map(int,input().split())
Dh,Dw=map(int,input().split())
s=[list(input()) for _ in range(h)]

Ch,Cw=Ch-1,Cw-1
Dh,Dw=Dh-1,Dw-1
from heapq import heappop,heappush
todo=[[0,Ch,Cw]]
d=[[-1]*w for _ in range(h)]
d[Ch][Cw]=0
toho=[[0,1],[0,-1],[1,0],[-1,0]]
wiz=[[2,2],[2,1],[2,0],[2,-1],[2,-2],[1,2],[1,1],[1,-1],[1,-2],[0,2],[0,-2],[-1,2],[-1,1],[-1,-1],[-1,-2],[-2,2],[-2,1],[-2,0],[-2,-1],[-2,-2]]
while todo:
  cnt,nh,nw=heappop(todo)
  for dh,dw in toho:
    if 0<=nh+dh<h and 0<=nw+dw<w and s[nh+dh][nw+dw]!='#':
      if d[nh+dh][nw+dw]==-1 or d[nh+dh][nw+dw]>cnt:
        d[nh+dh][nw+dw]=cnt
        heappush(todo,[cnt,nh+dh,nw+dw])
  for dh,dw in wiz:
    if 0<=nh+dh<h and 0<=nw+dw<w and s[nh+dh][nw+dw]!='#':
      if d[nh+dh][nw+dw]==-1 or d[nh+dh][nw+dw]>cnt+1:
        d[nh+dh][nw+dw]=cnt+1
        heappush(todo,[cnt+1,nh+dh,nw+dw])
print(d[Dh][Dw])


Fixed submission:
h,w=map(int,input().split())
Ch,Cw=map(int,input().split())
Dh,Dw=map(int,input().split())
s=[list(input()) for _ in range(h)]

Ch,Cw=Ch-1,Cw-1
Dh,Dw=Dh-1,Dw-1
todo=[[0,Ch,Cw]]
ntodo=[]
d=[[-1]*w for _ in range(h)]
d[Ch][Cw]=0
toho=[[0,1],[0,-1],[1,0],[-1,0]]
wiz=[[2,2],[2,1],[2,0],[2,-1],[2,-2],[1,2],[1,1],[1,-1],[1,-2],[0,2],[0,-2],[-1,2],[-1,1],[-1,-1],[-1,-2],[-2,2],[-2,1],[-2,0],[-2,-1],[-2,-2]]
while todo or ntodo:
  if not todo:
    todo=ntodo
    ntodo=[]
  cnt,nh,nw=todo.pop()
  if d[nh][nw]<cnt:continue
  for dh,dw in toho:
    if 0<=nh+dh<h and 0<=nw+dw<w and s[nh+dh][nw+dw]!='#':
      if d[nh+dh][nw+dw]==-1 or d[nh+dh][nw+dw]>cnt:
        d[nh+dh][nw+dw]=cnt
        todo.append([cnt,nh+dh,nw+dw])
  for dh,dw in wiz:
    if 0<=nh+dh<h and 0<=nw+dw<w and s[nh+dh][nw+dw]!='#':
      if d[nh+dh][nw+dw]==-1 or d[nh+dh][nw+dw]>cnt+1:
        d[nh+dh][nw+dw]=cnt+1
        ntodo.append([cnt+1,nh+dh,nw+dw])
print(d[Dh][Dw])