Buggy python submission (verdict: Time Limit Exceeded):
import heapq

def resolve():
    H,W = map(int,input().split())
    Sy,Sx = [int(i)-1 for i in input().split()]
    Gy,Gx = [int(i)-1 for i in input().split()]

    MP = [input() for i in range(H)]
    q =[]
    mxxx = 10**10
    score=[[mxxx]*W  for i in range(H)]
    score[Sy][Sx] = 0
    heapq.heappush(q,(0,Sx,Sy))
    visited = [[False for j in range(W)] for i in range(H)]

    while q:
        cs,x,y = heapq.heappop(q) 

        if visited[y][x]:
            continue
        visited[y][x]=True


        if y!=0 and MP[y-1][x]=='.' and score[y][x]<score[y-1][x]:

            score[y-1][x]=score[y][x]
            heapq.heappush(q,(cs,x,y-1))
        if y!=H-1 and MP[y+1][x]=='.' and score[y][x]<score[y+1][x]:


            score[y+1][x]=score[y][x]
            heapq.heappush(q,(cs,x,y+1))
  
        if x!=0 and MP[y][x-1]=='.' and score[y][x]<score[y][x-1]:

            score[y][x-1]=score[y][x]
            heapq.heappush(q,(cs,x-1,y))
        if x!=W-1 and MP[y][x+1]=='.' and score[y][x]<score[y][x+1]:

            score[y][x+1]=score[y][x]
            heapq.heappush(q,(cs,x+1,y))


        for i in range(max(0,y-2),min(H,y+3)):
            for j in range(max(0,x-2),min(W,x+3)):

                if MP[i][j]=='#':
                    continue
                if score[i][j]>score[y][x]+1:
                    score[i][j]=score[y][x]+1
                    heapq.heappush(q,(cs+1,j,i))

    if score[Gy][Gx]==mxxx:
        print(-1)
    else:
        print(score[Gy][Gx])
    
resolve()


Fixed submission:
from collections import deque

def resolve():
    H,W = map(int,input().split())
    Sy,Sx = [int(i)-1 for i in input().split()]
    Gy,Gx = [int(i)-1 for i in input().split()]

    MP = [input() for i in range(H)]
    q =[]
    mxxx = 10**10
    score=[[mxxx]*W  for i in range(H)]
    score[Sy][Sx] = 0
    deq = deque()
    deq.append((Sy,Sx))
    unvisited=set()
    for y,row in enumerate(MP):
        for x,i in enumerate(row):
            if i ==".":
                unvisited.add((y,x))

    while deq:
        y,x = deq.popleft()
        if not (y,x) in unvisited:
            continue
        unvisited.remove((y,x))

        if (y-1,x) in unvisited and score[y-1][x]>score[y][x]:
            score[y-1][x]=score[y][x]
            deq.appendleft((y-1,x))
        if (y+1,x) in unvisited and score[y+1][x]>score[y][x]:
            score[y+1][x]=score[y][x]
            deq.appendleft((y+1,x))
        if (y,x-1) in unvisited and score[y][x-1]>score[y][x]:
            score[y][x-1]=score[y][x]
            deq.appendleft((y,x-1))
        if (y,x+1) in unvisited and score[y][x+1]>score[y][x]:
            score[y][x+1]=score[y][x]
            deq.appendleft((y,x+1))

        for i in range(y-2,y+3):
            for j in range(x-2,x+3):
                if (i,j) in unvisited and score[i][j] > score[y][x]+1:
                    score[i][j] = score[y][x]+1
                    deq.append((i,j))
    
    if score[Gy][Gx] == 10**10:
        print(-1)
    else:
        print(score[Gy][Gx])




    
resolve()

Buggy python submission (verdict: Time Limit Exceeded):
import heapq

def resolve():
    H,W = map(int,input().split())
    Sy,Sx = [int(i)-1 for i in input().split()]
    Gy,Gx = [int(i)-1 for i in input().split()]

    MP = [input() for i in range(H)]
    q =[]
    score=[[10**10]*W  for i in range(H)]
    score[Sy][Sx] = 0
    heapq.heappush(q,(0,Sx,Sy))
    visited = [[False for j in range(W)] for i in range(H)]

    while q:
        cs,x,y = heapq.heappop(q) 

        if visited[y][x]:
            continue
        visited[y][x]=True


        if y!=0 and MP[y-1][x]=='.' and score[y][x]<score[y-1][x]:

            score[y-1][x]=score[y][x]
            heapq.heappush(q,(cs,x,y-1))
        if y!=H-1 and MP[y+1][x]=='.' and score[y][x]<score[y+1][x]:


            score[y+1][x]=score[y][x]
            heapq.heappush(q,(cs,x,y+1))
  
        if x!=0 and MP[y][x-1]=='.' and score[y][x]<score[y][x-1]:

            score[y][x-1]=score[y][x]
            heapq.heappush(q,(cs,x-1,y))
        if x!=W-1 and MP[y][x+1]=='.' and score[y][x]<score[y][x+1]:

            score[y][x+1]=score[y][x]
            heapq.heappush(q,(cs,x+1,y))


        for i in range(max(0,y-2),min(H,y+3)):
            for j in range(max(0,x-2),min(W,x+3)):

                if MP[i][j]=='#':
                    continue
                if score[i][j]>score[y][x]+1:
                    score[i][j]=score[y][x]+1
                    heapq.heappush(q,(cs+1,j,i))

    if score[Gy][Gx]==10**10:
        print(-1)
    else:
        print(score[Gy][Gx])
    
resolve()


Fixed submission:
from collections import deque

def resolve():
    H,W = map(int,input().split())
    Sy,Sx = [int(i)-1 for i in input().split()]
    Gy,Gx = [int(i)-1 for i in input().split()]

    MP = [input() for i in range(H)]
    q =[]
    mxxx = 10**10
    score=[[mxxx]*W  for i in range(H)]
    score[Sy][Sx] = 0
    deq = deque()
    deq.append((Sy,Sx))
    unvisited=set()
    for y,row in enumerate(MP):
        for x,i in enumerate(row):
            if i ==".":
                unvisited.add((y,x))

    while deq:
        y,x = deq.popleft()
        if not (y,x) in unvisited:
            continue
        unvisited.remove((y,x))

        if (y-1,x) in unvisited and score[y-1][x]>score[y][x]:
            score[y-1][x]=score[y][x]
            deq.appendleft((y-1,x))
        if (y+1,x) in unvisited and score[y+1][x]>score[y][x]:
            score[y+1][x]=score[y][x]
            deq.appendleft((y+1,x))
        if (y,x-1) in unvisited and score[y][x-1]>score[y][x]:
            score[y][x-1]=score[y][x]
            deq.appendleft((y,x-1))
        if (y,x+1) in unvisited and score[y][x+1]>score[y][x]:
            score[y][x+1]=score[y][x]
            deq.appendleft((y,x+1))

        for i in range(y-2,y+3):
            for j in range(x-2,x+3):
                if (i,j) in unvisited and score[i][j] > score[y][x]+1:
                    score[i][j] = score[y][x]+1
                    deq.append((i,j))
    
    if score[Gy][Gx] == 10**10:
        print(-1)
    else:
        print(score[Gy][Gx])




    
resolve()