Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline
 
h,w = list(map(int,input().split()))
s1,s2 = list(map(int,input().split()))
f1,f2 = list(map(int,input().split()))
 
s1,s2 = s1-1,s2-1
f1,f2 = f1-1,f2-1
 
Q = [(s1,s2)]
V = [[0]*w for _ in range(h)]
G = []
ALL = [(s1,s2)]
V[s1][s2] = 1
 
for _ in range(h):
  tmp = list(input().rstrip())
  G.append(tmp)
 
count = 0
best = 0
 
while True:
  while Q:
    new_Q = []
    for node in Q:
      i,j = node[0], node[1]
      if V[i][j]==0:
        ALL.append((i,j))

      if i-1>0:
        if V[i-1][j]==0 and G[i-1][j]=='.':
          V[i-1][j]=1
          new_Q.append((i-1,j))
          ALL.append((i-1,j))
 
      if j-1>0:
        if V[i][j-1]==0 and G[i][j-1]=='.':
          V[i][j-1]=1
          new_Q.append((i,j-1))
          ALL.append((i,j-1))
 
      if i+1<h:
        if V[i+1][j]==0 and G[i+1][j]=='.':
          V[i+1][j]=1
          new_Q.append((i+1,j))
          ALL.append((i+1,j))
 
      if j+1<w:
        if V[i][j+1]==0 and G[i][j+1]=='.':
          V[i][j+1]=1
          new_Q.append((i,j+1))
          ALL.append((i,j+1))
 
    Q = new_Q
 
  if V[f1][f2]==1:
    print(count)
    break
  else:
    count += 1
    part= []
    
    ALL = list(set(ALL))
 
    for node in ALL:
      i,j = node[0], node[1]
      
      for x in range(i-2,i+3):
        for y in range(j-2,j+3):
          if x>-1 and y>-1 and x<h and y<w and G[x][y] == '.' and V[x][y]==0:
            part.append((x,y))         	
       
    ALL = list(set(part))
    #print(ALL)
    Q = list(ALL)
    
    if (f1,f2) in ALL:
      print(count)
      break
 
    if len(ALL)==0:
      print(-1)
      break
      
    ALL = []
        


Fixed submission:
import sys
input = sys.stdin.readline
 
h,w = list(map(int,input().split()))
s1,s2 = list(map(int,input().split()))
f1,f2 = list(map(int,input().split()))
 
s1,s2 = s1-1,s2-1
f1,f2 = f1-1,f2-1
 
Q = [(s1,s2)]
V = [[0]*w for _ in range(h)]
G = []
ALL = [(s1,s2)]
V[s1][s2] = 1
 
for _ in range(h):
  tmp = list(input().rstrip())
  G.append(tmp)
 
count = 0
best = 0
 
while True:
  while Q:
    new_Q = []
    for node in Q:
      i,j = node[0], node[1]
      if V[i][j]==0:
        ALL.append((i,j))
        V[i][j] = 1

      if i-1>0:
        if V[i-1][j]==0 and G[i-1][j]=='.':
          V[i-1][j]=1
          new_Q.append((i-1,j))
          ALL.append((i-1,j))
 
      if j-1>0:
        if V[i][j-1]==0 and G[i][j-1]=='.':
          V[i][j-1]=1
          new_Q.append((i,j-1))
          ALL.append((i,j-1))
 
      if i+1<h:
        if V[i+1][j]==0 and G[i+1][j]=='.':
          V[i+1][j]=1
          new_Q.append((i+1,j))
          ALL.append((i+1,j))
 
      if j+1<w:
        if V[i][j+1]==0 and G[i][j+1]=='.':
          V[i][j+1]=1
          new_Q.append((i,j+1))
          ALL.append((i,j+1))
 
    Q = new_Q
 
  if V[f1][f2]==1:
    print(count)
    break
  else:
    count += 1
    part= []
    
    ALL = list(set(ALL))
 
    for node in ALL:
      i,j = node[0], node[1]
      
      for x in range(i-2,i+3):
        for y in range(j-2,j+3):
          if x>-1 and y>-1 and x<h and y<w and G[x][y] == '.' and V[x][y]==0:
            part.append((x,y))         	
       
    ALL = list(set(part))
    #print(ALL)
    Q = list(ALL)
    
    if (f1,f2) in ALL:
      print(count)
      break
 
    if len(ALL)==0:
      print(-1)
      break
      
    ALL = []

Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline
 
h,w = list(map(int,input().split()))
s1,s2 = list(map(int,input().split()))
f1,f2 = list(map(int,input().split()))
 
s1,s2 = s1-1,s2-1
f1,f2 = f1-1,f2-1
 
Q = [(s1,s2)]
V = [[0]*w for _ in range(h)]
G = []
ALL = [(s1,s2)]
V[s1][s2] = 1
 
for _ in range(h):
  tmp = list(input().rstrip())
  G.append(tmp)
 
count = 0
best = 0
 
while True:
  while Q:
    new_Q = []
    for node in Q:
      i,j = node[0], node[1]
      if i-1>0:
        if V[i-1][j]==0 and G[i-1][j]=='.':
          V[i-1][j]=1
          new_Q.append((i-1,j))
          ALL.append((i-1,j))
 
      if j-1>0:
        if V[i][j-1]==0 and G[i][j-1]=='.':
          V[i][j-1]=1
          new_Q.append((i,j-1))
          ALL.append((i,j-1))
 
      if i+1<h:
        if V[i+1][j]==0 and G[i+1][j]=='.':
          V[i+1][j]=1
          new_Q.append((i+1,j))
          ALL.append((i+1,j))
 
      if j+1<w:
        if V[i][j+1]==0 and G[i][j+1]=='.':
          V[i][j+1]=1
          new_Q.append((i,j+1))
          ALL.append((i,j+1))
 
    Q = new_Q
 
  if V[f1][f2]==1:
    print(count)
    break
  else:
    count += 1
    part= []
    
    ALL = list(set(ALL))
    BE = {}
    
    for node in ALL:
      i,j = node[0], node[1]
      
      for x in range(i-2,i+3):
        for y in range(j-2,j+3):
          if (x,y) not in BE:
            BE[(x,y)] = 1
            if x>-1 and y>-1 and x<h and y<w and G[x][y] == '.' and V[x][y]==0:
              part.append((x,y))         	
       
    ALL = list(part)
    Q = list(ALL)
 
    if (f1,f2) in ALL:
      print(count)
      break
 
    if len(ALL)==0:
      print(-1)
      break

Fixed submission:
import sys
input = sys.stdin.readline
 
h,w = list(map(int,input().split()))
s1,s2 = list(map(int,input().split()))
f1,f2 = list(map(int,input().split()))
 
s1,s2 = s1-1,s2-1
f1,f2 = f1-1,f2-1
 
Q = [(s1,s2)]
V = [[0]*w for _ in range(h)]
G = []
ALL = [(s1,s2)]
V[s1][s2] = 1
 
for _ in range(h):
  tmp = list(input().rstrip())
  G.append(tmp)
 
count = 0
best = 0
 
while True:
  while Q:
    new_Q = []
    for node in Q:
      i,j = node[0], node[1]
      if V[i][j]==0:
        ALL.append((i,j))
        V[i][j] = 1

      if i-1>0:
        if V[i-1][j]==0 and G[i-1][j]=='.':
          V[i-1][j]=1
          new_Q.append((i-1,j))
          ALL.append((i-1,j))
 
      if j-1>0:
        if V[i][j-1]==0 and G[i][j-1]=='.':
          V[i][j-1]=1
          new_Q.append((i,j-1))
          ALL.append((i,j-1))
 
      if i+1<h:
        if V[i+1][j]==0 and G[i+1][j]=='.':
          V[i+1][j]=1
          new_Q.append((i+1,j))
          ALL.append((i+1,j))
 
      if j+1<w:
        if V[i][j+1]==0 and G[i][j+1]=='.':
          V[i][j+1]=1
          new_Q.append((i,j+1))
          ALL.append((i,j+1))
 
    Q = new_Q
 
  if V[f1][f2]==1:
    print(count)
    break
  else:
    count += 1
    part= []
    
    ALL = list(set(ALL))
 
    for node in ALL:
      i,j = node[0], node[1]
      
      for x in range(i-2,i+3):
        for y in range(j-2,j+3):
          if x>-1 and y>-1 and x<h and y<w and G[x][y] == '.' and V[x][y]==0:
            part.append((x,y))         	
       
    ALL = list(set(part))
    #print(ALL)
    Q = list(ALL)
    
    if (f1,f2) in ALL:
      print(count)
      break
 
    if len(ALL)==0:
      print(-1)
      break
      
    ALL = []

Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline

h,w = list(map(int,input().split()))
s1,s2 = list(map(int,input().split()))
f1,f2 = list(map(int,input().split()))

s1,s2 = s1-1,s2-1
f1,f2 = f1-1,f2-1

Q = [(s1,s2)]
V = [[0]*w for _ in range(h)]
G = []
ALL = [(s1,s2)]
V[s1][s2] = 1

for _ in range(h):
  tmp = list(input().rstrip())
  G.append(tmp)

count = 0
best = 0

while True:
  while Q:
    new_Q = []
    for node in Q:
      i,j = node[0], node[1]
      if i-1>0:
        if V[i-1][j]==0 and G[i-1][j]=='.':
          V[i-1][j]=1
          new_Q.append((i-1,j))
          ALL.append((i-1,j))

      if j-1>0:
        if V[i][j-1]==0 and G[i][j-1]=='.':
          V[i][j-1]=1
          new_Q.append((i,j-1))
          ALL.append((i,j-1))

      if i+1<h:
        if V[i+1][j]==0 and G[i+1][j]=='.':
          V[i+1][j]=1
          new_Q.append((i+1,j))
          ALL.append((i+1,j))

      if j+1<w:
        if V[i][j+1]==0 and G[i][j+1]=='.':
          V[i][j+1]=1
          new_Q.append((i,j+1))
          ALL.append((i,j+1))

    Q = new_Q

  if V[f1][f2]==1:
    print(count)
    break
  else:
    count += 1
    part= []
    
    ALL = list(set(ALL))
    
    for node in ALL:
      i,j = node[0], node[1]
      
      for x in range(i-2,i+3):
        for y in range(j-2,j+3):
          if x>-1 and y>-1 and x<h and y<w and G[x][y] == '.' and V[x][y]==0:
            part.append((x,y))         	
       
    ALL = list(set(part))
    Q = list(ALL)

    if (f1,f2) in ALL:
      print(count)
      break

    if len(ALL)==0:
      print(-1)
      break
        

Fixed submission:
import sys
input = sys.stdin.readline
 
h,w = list(map(int,input().split()))
s1,s2 = list(map(int,input().split()))
f1,f2 = list(map(int,input().split()))
 
s1,s2 = s1-1,s2-1
f1,f2 = f1-1,f2-1
 
Q = [(s1,s2)]
V = [[0]*w for _ in range(h)]
G = []
ALL = [(s1,s2)]
V[s1][s2] = 1
 
for _ in range(h):
  tmp = list(input().rstrip())
  G.append(tmp)
 
count = 0
best = 0
 
while True:
  while Q:
    new_Q = []
    for node in Q:
      i,j = node[0], node[1]
      if V[i][j]==0:
        ALL.append((i,j))
        V[i][j] = 1

      if i-1>0:
        if V[i-1][j]==0 and G[i-1][j]=='.':
          V[i-1][j]=1
          new_Q.append((i-1,j))
          ALL.append((i-1,j))
 
      if j-1>0:
        if V[i][j-1]==0 and G[i][j-1]=='.':
          V[i][j-1]=1
          new_Q.append((i,j-1))
          ALL.append((i,j-1))
 
      if i+1<h:
        if V[i+1][j]==0 and G[i+1][j]=='.':
          V[i+1][j]=1
          new_Q.append((i+1,j))
          ALL.append((i+1,j))
 
      if j+1<w:
        if V[i][j+1]==0 and G[i][j+1]=='.':
          V[i][j+1]=1
          new_Q.append((i,j+1))
          ALL.append((i,j+1))
 
    Q = new_Q
 
  if V[f1][f2]==1:
    print(count)
    break
  else:
    count += 1
    part= []
    
    ALL = list(set(ALL))
 
    for node in ALL:
      i,j = node[0], node[1]
      
      for x in range(i-2,i+3):
        for y in range(j-2,j+3):
          if x>-1 and y>-1 and x<h and y<w and G[x][y] == '.' and V[x][y]==0:
            part.append((x,y))         	
       
    ALL = list(set(part))
    #print(ALL)
    Q = list(ALL)
    
    if (f1,f2) in ALL:
      print(count)
      break
 
    if len(ALL)==0:
      print(-1)
      break
      
    ALL = []

Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline

h,w = list(map(int,input().split()))
s1,s2 = list(map(int,input().split()))
f1,f2 = list(map(int,input().split()))

s1,s2 = s1-1,s2-1
f1,f2 = f1-1,f2-1

Q = [(s1,s2)]
V = [[0]*w for _ in range(h)]
G = []
ALL = [(s1,s2)]
V[s1][s2] = 1

for _ in range(h):
  tmp = list(input().rstrip())
  G.append(tmp)

count = 0
best = 0

while True:
  while Q:
    new_Q = []
    for node in Q:
      i,j = node[0], node[1]
      if i-1>0:
        if V[i-1][j]==0 and G[i-1][j]=='.':
          V[i-1][j]=1
          new_Q.append((i-1,j))
          ALL.append((i-1,j))

      if j-1>0:
        if V[i][j-1]==0 and G[i][j-1]=='.':
          V[i][j-1]=1
          new_Q.append((i,j-1))
          ALL.append((i,j-1))

      if i+1<h:
        if V[i+1][j]==0 and G[i+1][j]=='.':
          V[i+1][j]=1
          new_Q.append((i+1,j))
          ALL.append((i+1,j))

      if j+1<w:
        if V[i][j+1]==0 and G[i][j+1]=='.':
          V[i][j+1]=1
          new_Q.append((i,j+1))
          ALL.append((i,j+1))

    Q = new_Q

  if V[f1][f2]==1:
    print(count)
    break
  else:
    count += 1
    part= []
    
    for node in ALL:
      i,j = node[0], node[1]
      
      for x in range(i-2,i+3):
        for y in range(j-2,j+3):
          if x>-1 and y>-1 and x<h and y<w:
            if G[x][y] == '.' and V[x][y]==0:
              part.append((x,y))
       
    ALL = list(set(part))
    Q = list(ALL)
    
    #print(temp,best)
    if (f1,f2) in ALL:
      print(count)
      break

    if len(ALL)==0:
      print(-1)
      break
        


Fixed submission:
import sys
input = sys.stdin.readline
 
h,w = list(map(int,input().split()))
s1,s2 = list(map(int,input().split()))
f1,f2 = list(map(int,input().split()))
 
s1,s2 = s1-1,s2-1
f1,f2 = f1-1,f2-1
 
Q = [(s1,s2)]
V = [[0]*w for _ in range(h)]
G = []
ALL = [(s1,s2)]
V[s1][s2] = 1
 
for _ in range(h):
  tmp = list(input().rstrip())
  G.append(tmp)
 
count = 0
best = 0
 
while True:
  while Q:
    new_Q = []
    for node in Q:
      i,j = node[0], node[1]
      if V[i][j]==0:
        ALL.append((i,j))
        V[i][j] = 1

      if i-1>0:
        if V[i-1][j]==0 and G[i-1][j]=='.':
          V[i-1][j]=1
          new_Q.append((i-1,j))
          ALL.append((i-1,j))
 
      if j-1>0:
        if V[i][j-1]==0 and G[i][j-1]=='.':
          V[i][j-1]=1
          new_Q.append((i,j-1))
          ALL.append((i,j-1))
 
      if i+1<h:
        if V[i+1][j]==0 and G[i+1][j]=='.':
          V[i+1][j]=1
          new_Q.append((i+1,j))
          ALL.append((i+1,j))
 
      if j+1<w:
        if V[i][j+1]==0 and G[i][j+1]=='.':
          V[i][j+1]=1
          new_Q.append((i,j+1))
          ALL.append((i,j+1))
 
    Q = new_Q
 
  if V[f1][f2]==1:
    print(count)
    break
  else:
    count += 1
    part= []
    
    ALL = list(set(ALL))
 
    for node in ALL:
      i,j = node[0], node[1]
      
      for x in range(i-2,i+3):
        for y in range(j-2,j+3):
          if x>-1 and y>-1 and x<h and y<w and G[x][y] == '.' and V[x][y]==0:
            part.append((x,y))         	
       
    ALL = list(set(part))
    #print(ALL)
    Q = list(ALL)
    
    if (f1,f2) in ALL:
      print(count)
      break
 
    if len(ALL)==0:
      print(-1)
      break
      
    ALL = []

Buggy python submission (verdict: Time Limit Exceeded):
import sys
input = sys.stdin.readline

h,w = list(map(int,input().split()))
s1,s2 = list(map(int,input().split()))
f1,f2 = list(map(int,input().split()))

s1,s2 = s1-1,s2-1
f1,f2 = f1-1,f2-1

Q = [(s1,s2)]
V = [[0]*w for _ in range(h)]
G = []
ALL = [(s1,s2)]
V[s1][s2] = 1

for _ in range(h):
  tmp = list(input().rstrip())
  G.append(tmp)

count = 0
best = 0

while True:
  while Q:
    new_Q = []
    for node in Q:
      #print(node)
      i,j = node[0], node[1]
      if i-1>0:
        if V[i-1][j]==0 and G[i-1][j]=='.':
          V[i-1][j]=1
          new_Q.append((i-1,j))
          ALL.append((i-1,j))

      if j-1>0:
        if V[i][j-1]==0 and G[i][j-1]=='.':
          V[i][j-1]=1
          new_Q.append((i,j-1))
          ALL.append((i,j-1))

      if i+1<h:
        if V[i+1][j]==0 and G[i+1][j]=='.':
          V[i+1][j]=1
          new_Q.append((i+1,j))
          ALL.append((i+1,j))

      if j+1<w:
        if V[i][j+1]==0 and G[i][j+1]=='.':
          V[i][j+1]=1
          new_Q.append((i,j+1))
          ALL.append((i,j+1))

    Q = new_Q

  #print(f1,f2)
  if V[f1][f2]==1:
    print(count)
    break
  else:
    #print(V)
    temp = sum(sum(kk) for kk in V) 
    count += 1
    #print(ALL,best,temp)
    part= []
    
    for node in ALL:
      i,j = node[0], node[1]
      
      for x in range(i-2,i+3):
        for y in range(j-2,j+3):
          if x>-1 and y>-1 and x<h and y<w:
            if G[x][y] == '.':
              V[x][y] = 1
              part.append((x,y))
              
    part = list(set(part))
    ALL = part+ALL

    if temp==best:
      print(-1)
      break
    else:
      best = temp
  

Fixed submission:
import sys
input = sys.stdin.readline
 
h,w = list(map(int,input().split()))
s1,s2 = list(map(int,input().split()))
f1,f2 = list(map(int,input().split()))
 
s1,s2 = s1-1,s2-1
f1,f2 = f1-1,f2-1
 
Q = [(s1,s2)]
V = [[0]*w for _ in range(h)]
G = []
ALL = [(s1,s2)]
V[s1][s2] = 1
 
for _ in range(h):
  tmp = list(input().rstrip())
  G.append(tmp)
 
count = 0
best = 0
 
while True:
  while Q:
    new_Q = []
    for node in Q:
      i,j = node[0], node[1]
      if V[i][j]==0:
        ALL.append((i,j))
        V[i][j] = 1

      if i-1>0:
        if V[i-1][j]==0 and G[i-1][j]=='.':
          V[i-1][j]=1
          new_Q.append((i-1,j))
          ALL.append((i-1,j))
 
      if j-1>0:
        if V[i][j-1]==0 and G[i][j-1]=='.':
          V[i][j-1]=1
          new_Q.append((i,j-1))
          ALL.append((i,j-1))
 
      if i+1<h:
        if V[i+1][j]==0 and G[i+1][j]=='.':
          V[i+1][j]=1
          new_Q.append((i+1,j))
          ALL.append((i+1,j))
 
      if j+1<w:
        if V[i][j+1]==0 and G[i][j+1]=='.':
          V[i][j+1]=1
          new_Q.append((i,j+1))
          ALL.append((i,j+1))
 
    Q = new_Q
 
  if V[f1][f2]==1:
    print(count)
    break
  else:
    count += 1
    part= []
    
    ALL = list(set(ALL))
 
    for node in ALL:
      i,j = node[0], node[1]
      
      for x in range(i-2,i+3):
        for y in range(j-2,j+3):
          if x>-1 and y>-1 and x<h and y<w and G[x][y] == '.' and V[x][y]==0:
            part.append((x,y))         	
       
    ALL = list(set(part))
    #print(ALL)
    Q = list(ALL)
    
    if (f1,f2) in ALL:
      print(count)
      break
 
    if len(ALL)==0:
      print(-1)
      break
      
    ALL = []