Buggy python submission (verdict: Time Limit Exceeded):
def main(H,W,ch,cw,dh,dw,S):
    q=np.zeros((3*10**7,3),dtype=np.int32)
    v=-np.ones((H,W),dtype=np.int32)
    x=[[1,0],[-1,0],[0,-1],[0,1]]
    y=[[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]]
    l,r=5*10**6,5*10**6+1
    q[l][0],q[l][1],q[l][2]=ch-1,cw-1,0
    while l<r:
        h,w,d=q[l][0],q[l][1],q[l][2]
        l+=1
        if v[h][w]<0:
            v[h][w]=d
        for k in range(4):
            i,j=x[k][0],x[k][1]
            if 0<=h+i<H and 0<=w+j<W and S[h+i][w+j] and v[h+i][w+j]<0:
                l-=1
                q[l][0],q[l][1],q[l][2]=h+i,w+j,d
        for k in range(20):
            i,j=y[k][0],y[k][1]
            if 0<=h+i<H and 0<=w+j<W and S[h+i][w+j] and v[h+i][w+j]<0:
                q[r][0],q[r][1],q[r][2]=h+i,w+j,d+1
                r+=1
    return v[dh-1][dw-1]
import sys
import numpy as np
readline=sys.stdin.buffer.readline
read=sys.stdin.buffer.read
if sys.argv[-1]=='ONLINE_JUDGE':
    from numba import*
    from numba.pycc import CC
    cc=CC('my_module')
    def cc_export(f,s):
        cc.export(f.__name__,s)(f)
        return njit(f)
    main=cc_export(main,(i4,i4,i4,i4,i4,i4,i4[:,:]))
    cc.compile()
    exit()
H,W=map(int,readline().split())
ch,cw=map(int,readline().split())
dh,dw=map(int,readline().split())
S=np.array([[1 if c==ord('.') else 0 for c in readline().strip()] for i in range(H)],dtype=np.int32)
from my_module import main
print(main(H,W,ch,cw,dh,dw,S))


Fixed submission:
H,W=map(int,input().split())
ch,cw=map(int,input().split())
dh,dw=map(int,input().split())
S=[input() for i in range(H)]
from collections import deque
q=deque([(ch-1,cw-1,0)])
v=[[9**9]*W for i in range(H)]
x=((1,0),(-1,0),(0,-1),(0,1))
y=((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 q:
    h,w,d=q.popleft()
    for i,j in x:
        if 0<=h+i<H and 0<=w+j<W and S[h+i][w+j]=='.' and d<v[h+i][w+j]:
            v[h+i][w+j]=d
            q.appendleft((h+i,w+j,d))
    for i,j in y:
        if 0<=h+i<H and 0<=w+j<W and S[h+i][w+j]=='.' and d+1<v[h+i][w+j]:
            v[h+i][w+j]=d+1
            q.append((h+i,w+j,d+1))
print(v[dh-1][dw-1] if v[dh-1][dw-1]<9**9 else -1)

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=[input() for i in range(H)]
from collections import deque
q=deque([(ch-1,cw-1,0)])
v=[[-1]*W for i in range(H)]
x=((1,0),(-1,0),(0,-1),(0,1))
y=((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 q:
    h,w,d=q.popleft()
    if v[h][w]<0:
        v[h][w]=d
    for i,j in x:
        if 0<=h+i<H and 0<=w+j<W and S[h+i][w+j]=='.' and v[h+i][w+j]<0:
            q.appendleft((h+i,w+j,d))
    for i,j in y:
        if 0<=h+i<H and 0<=w+j<W and S[h+i][w+j]=='.' and v[h+i][w+j]<0:
            q.append((h+i,w+j,d+1))
print(v[dh-1][dw-1])

Fixed submission:
H,W=map(int,input().split())
ch,cw=map(int,input().split())
dh,dw=map(int,input().split())
S=[input() for i in range(H)]
from collections import deque
q=deque([(ch-1,cw-1,0)])
v=[[9**9]*W for i in range(H)]
x=((1,0),(-1,0),(0,-1),(0,1))
y=((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 q:
    h,w,d=q.popleft()
    for i,j in x:
        if 0<=h+i<H and 0<=w+j<W and S[h+i][w+j]=='.' and d<v[h+i][w+j]:
            v[h+i][w+j]=d
            q.appendleft((h+i,w+j,d))
    for i,j in y:
        if 0<=h+i<H and 0<=w+j<W and S[h+i][w+j]=='.' and d+1<v[h+i][w+j]:
            v[h+i][w+j]=d+1
            q.append((h+i,w+j,d+1))
print(v[dh-1][dw-1] if v[dh-1][dw-1]<9**9 else -1)