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())
Ch -= 1
Cw -= 1
Dh -= 1
Dw -= 1

squares = []
for i in range(H):
    squares.append([None]*(W))

for i in range(H):
    s = input()
    for j in range(W):
        if s[j] == '#':
            squares[i][j] = -1  # Wall

squares[Ch][Cw]=0

d = deque()
d.append([Ch, Cw])

steps = [[-1,0],[1,0],[0,-1],[0,1]]

warps = 0

def visit(i1, j1, i2, j2):  # (i1,j1) to (i2,j2)
    if i2 < 0 or i2 >= H or j2 < 0 or j2 >= W:
        return
    sq2 = squares[i2][j2]
    if sq2 == -1:
        return
    if sq2 == None:
        squares[i2][j2] = warps  # sq2 = warps <- doesn't work
        d.append([i2, j2])
        if i2 == Dh and j2 == Dw:
            print(warps)
            exit()

while (len(d)>0):
    while (len(d)>0):
        src = d.popleft()
        for st in steps:
            visit(src[0], src[1], src[0]+st[0], src[1]+st[1])
    warps += 1
    for i in range(H):
        for j in range(W):
            sq = squares[i][j]
            if sq == warps - 1:
                for di in range(-2,3):
                    for dj in range(-2,3):
                        visit(i, j, i+di, j+dj)

print(-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())
Ch -= 1
Cw -= 1
Dh -= 1
Dw -= 1

squares = []
for i in range(H):
    squares.append([None]*(W))

for i in range(H):
    s = input()
    for j in range(W):
        if s[j] == '#':
            squares[i][j] = -1  # Wall

squares[Ch][Cw]=0

d1 = deque()
d2 = deque()
d1.append([Ch, Cw])

warps = 0

def visit(i1, j1, i2, j2, with_warp = False):  # (i1,j1) to (i2,j2)
    if i2 < 0 or i2 >= H or j2 < 0 or j2 >= W:
        return
    sq2 = squares[i2][j2]
    if sq2 == None:
        if with_warp:
            squares[i2][j2] = warps + 1  # sq2 = warps + 1 <- doesn't work
        else:
            squares[i2][j2] = warps  # sq2 = warps <- doesn't work
        d1.append([i2, j2])
        if i2 == Dh and j2 == Dw:
            print(squares[i2][j2])
            exit()

while (len(d1)>0):
    while (len(d1)>0):
        src = d1.popleft()
        visit(src[0], src[1], src[0] - 1, src[1])
        visit(src[0], src[1], src[0] + 1, src[1])
        visit(src[0], src[1], src[0], src[1] - 1)
        visit(src[0], src[1], src[0], src[1] + 1)
        d2.append(src)

    while (len(d2)>0):
        src = d2.popleft()
        for i in range(-2,3):
            for j in range(-2,3):
                visit(src[0], src[1], src[0]+i, src[1]+j, True)

    warps += 1

print(-1)

Buggy python submission (verdict: Time Limit Exceeded):
H,W = map(int, input().strip().split())
Ch, Cw = map(int, input().strip().split())
Dh, Dw = map(int, input().strip().split())
Ch += 1
Cw += 1
Dh += 1
Dw += 1

moves=[]
for i in range(H+4):
    moves.append([1000000]*(W+4))

for i in range(2,H+2):
    s = input().strip()
    for j in range(W):
        if s[j] == '#':
            moves[i][j+2] = -1

for i in range(H+4):
    for j in range(W+4):
        if i<=1 or i>=H+2 or j<=1 or j>=W+2:
            moves[i][j]=-1


moves[Ch][Cw]=0
sources_0 = [[-1,0],[1,0],[0,-1],[0,1]]
sources_1 = [[-2,-2],[-1,-2],[0,-2],[1,-2],[2,-2]]
sources_1 += [[-2,-1],[-1,-1],[0,-1],[1,-1],[2,-1]]
sources_1 += [[-2,0],[-1,0],[1,0],[2,0]]
sources_1 += [[-2,1],[-1,1],[0,1],[1,1],[2,1]]
sources_1 += [[-2,2],[-1,2],[0,2],[1,2],[2,2]]

n = 0
while (n <= H*W):
    n += 1
    for i in range(2,H+2):
        for j in range(2,W+2):
            if moves[i][j] <= 0:
                continue
            for src in sources_0:
                src_move = moves[i+src[0]][j+src[1]]
                if src_move >= 0 and src_move < moves[i][j]:
                    moves[i][j] = src_move
            for src in sources_1:
                src_move = moves[i+src[0]][j+src[1]]
                if src_move >= 0 and src_move + 1 < moves[i][j]:
                    moves[i][j] = src_move + 1

if moves[Dh][Dw] == 1000000:
    print(-1)
else:
    print(moves[Dh][Dw])

Fixed submission:
from collections import deque

H,W = map(int, input().split())
Ch, Cw = map(int, input().split())
Dh, Dw = map(int, input().split())
Ch -= 1
Cw -= 1
Dh -= 1
Dw -= 1

squares = []
for i in range(H):
    squares.append([None]*(W))

for i in range(H):
    s = input()
    for j in range(W):
        if s[j] == '#':
            squares[i][j] = -1  # Wall

squares[Ch][Cw]=0

d1 = deque()
d2 = deque()
d1.append([Ch, Cw])

warps = 0

def visit(i1, j1, i2, j2, with_warp = False):  # (i1,j1) to (i2,j2)
    if i2 < 0 or i2 >= H or j2 < 0 or j2 >= W:
        return
    sq2 = squares[i2][j2]
    if sq2 == None:
        if with_warp:
            squares[i2][j2] = warps + 1  # sq2 = warps + 1 <- doesn't work
        else:
            squares[i2][j2] = warps  # sq2 = warps <- doesn't work
        d1.append([i2, j2])
        if i2 == Dh and j2 == Dw:
            print(squares[i2][j2])
            exit()

while (len(d1)>0):
    while (len(d1)>0):
        src = d1.popleft()
        visit(src[0], src[1], src[0] - 1, src[1])
        visit(src[0], src[1], src[0] + 1, src[1])
        visit(src[0], src[1], src[0], src[1] - 1)
        visit(src[0], src[1], src[0], src[1] + 1)
        d2.append(src)

    while (len(d2)>0):
        src = d2.popleft()
        for i in range(-2,3):
            for j in range(-2,3):
                visit(src[0], src[1], src[0]+i, src[1]+j, True)

    warps += 1

print(-1)

Buggy python submission (verdict: Time Limit Exceeded):
H,W = map(int, input().strip().split())
Ch, Cw = map(int, input().strip().split())
Dh, Dw = map(int, input().strip().split())
Ch -= 1
Cw -= 1
Dh -= 1
Dw -= 1

moves=[]
for i in range(H):
    moves.append([1000000]*W)

for i in range(H):
    s = input().strip()
    for j in range(W):
        if s[j] == '#':
            moves[i][j] = -1

moves[Ch][Cw]=0
sources_0 = [[-1,0],[1,0],[0,-1],[0,1]]
sources_1 = [[-2,-2],[-1,-2],[0,-2],[1,-2],[2,-2]]
sources_1 += [[-2,-1],[-1,-1],[0,-1],[1,-1],[2,-1]]
sources_1 += [[-2,0],[-1,0],[1,0],[2,0]]
sources_1 += [[-2,1],[-1,1],[0,1],[1,1],[2,1]]
sources_1 += [[-2,2],[-1,2],[0,2],[1,2],[2,2]]

def not_concluded():
    for i in range(H):
        for j in range(W):
            if moves[i][j] == 1000000:
                return True
    return False

n = 0
while (n <= H*W):
    n += 1
    for i in range(H):
        for j in range(W):
            if moves[i][j] <= 0:
                continue
            for src in sources_0:
                if i+src[0] >= 0 and i+src[0] < H and j+src[1] >= 0 and j+src[1] < W:
                    src_move = moves[i+src[0]][j+src[1]]
                    if src_move >= 0 and src_move < moves[i][j]:
                        moves[i][j] = src_move
            for src in sources_1:
                if i+src[0] >= 0 and i+src[0] < H and j+src[1] >= 0 and j+src[1] < W:
                    src_move = moves[i+src[0]][j+src[1]]
                    if src_move >= 0 and src_move + 1 < moves[i][j]:
                        moves[i][j] = src_move + 1

if moves[Dh][Dw] == 1000000:
    print(-1)
else:
    print(moves[Dh][Dw])

Fixed submission:
from collections import deque

H,W = map(int, input().split())
Ch, Cw = map(int, input().split())
Dh, Dw = map(int, input().split())
Ch -= 1
Cw -= 1
Dh -= 1
Dw -= 1

squares = []
for i in range(H):
    squares.append([None]*(W))

for i in range(H):
    s = input()
    for j in range(W):
        if s[j] == '#':
            squares[i][j] = -1  # Wall

squares[Ch][Cw]=0

d1 = deque()
d2 = deque()
d1.append([Ch, Cw])

warps = 0

def visit(i1, j1, i2, j2, with_warp = False):  # (i1,j1) to (i2,j2)
    if i2 < 0 or i2 >= H or j2 < 0 or j2 >= W:
        return
    sq2 = squares[i2][j2]
    if sq2 == None:
        if with_warp:
            squares[i2][j2] = warps + 1  # sq2 = warps + 1 <- doesn't work
        else:
            squares[i2][j2] = warps  # sq2 = warps <- doesn't work
        d1.append([i2, j2])
        if i2 == Dh and j2 == Dw:
            print(squares[i2][j2])
            exit()

while (len(d1)>0):
    while (len(d1)>0):
        src = d1.popleft()
        visit(src[0], src[1], src[0] - 1, src[1])
        visit(src[0], src[1], src[0] + 1, src[1])
        visit(src[0], src[1], src[0], src[1] - 1)
        visit(src[0], src[1], src[0], src[1] + 1)
        d2.append(src)

    while (len(d2)>0):
        src = d2.popleft()
        for i in range(-2,3):
            for j in range(-2,3):
                visit(src[0], src[1], src[0]+i, src[1]+j, True)

    warps += 1

print(-1)