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

h, w = map(int, input().split())
ch, cw = map(int, input().split())
gh, gw = map(int, input().split())

s = []
for i in range(h):
   s.append(input().rstrip('\n'))

INF = 10 ** 10
d = [INF] * (h*w)

stack = deque([(ch-1, cw-1, 0)])

nex = []
for i in range(-2, 3):
    for j in range(-2, 3):
        if (i, j) in [(-1,0),(1,0),(0,-1),(0,1),(0,0)]:
            continue
        else:
            nex.append((i,j))

while stack:
    curh, curw, cnt = stack.popleft()
    if d[curh * w + curw] <= cnt:
        continue
    else:
        d[curh * w + curw] = cnt
    for dh, dw in ((-1,0), (1,0), (0,1), (0,-1)):
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.' and d[nh * w + nw] > cnt:
            stack.appendleft((nh, nw, cnt))
    for dh, dw in nex:
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.' and  d[nh * w + nw] > cnt:
            stack.append((nh, nw, cnt+1))

# for item in d:
#     print(item)
gh -= 1
gw -= 1

if d[gh*w + gw] == INF:
    print(-1)
else:
    print(d[gh*w + gw])


Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

h, w = map(int, input().split())
ch, cw = map(int, input().split())
gh, gw = map(int, input().split())

s = []
for i in range(h):
   s.append(input().rstrip('\n'))

INF = 10 ** 10
d = [INF] * (h*w)

stack = deque([(ch-1, cw-1, 0)])
stack_append = stack.append
stack_popleft = stack.popleft

nex = []
for i in range(-2, 3):
    for j in range(-2, 3):
        if (i, j) in [(-1,0),(1,0),(0,-1),(0,1),(0,0)]:
            continue
        else:
            nex.append((i,j))

while stack:
    curh, curw, cnt = stack_popleft()
    if d[curh * w + curw] <= cnt:
        continue
    else:
        d[curh * w + curw] = cnt
    for dh, dw in ((-1,0), (1,0), (0,1), (0,-1)):
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.' and d[nh * w + nw] > cnt:
            stack_append((nh, nw, cnt))
    for dh, dw in nex:
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.' and  d[nh * w + nw] > cnt:
            stack_append((nh, nw, cnt+1))

# for item in d:
#     print(item)
gh -= 1
gw -= 1

if d[gh*w + gw] == INF:
    print(-1)
else:
    print(d[gh*w + gw])


Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

import heapq

INF = 10 ** 10

class Edge():
    def __init__(self, end, cost):
        self.end = end
        self.cost = cost

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for e in G[v]:
            if dist[e.end] > dist[v] + e.cost:
                dist[e.end] = dist[v] + e.cost
                heapq.heappush(h, (dist[e.end], e.end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend(Edge(b, 0))
                    else:
                        esappend(Edge(b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

import heapq

INF = 10 ** 10

class Edge():
    def __init__(self, end, cost):
        self.end = end
        self.cost = cost

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for e in G[v]:
            if dist[e.end] > dist[v] + e.cost:
                dist[e.end] = dist[v] + e.cost
                heapq.heappush(h, (dist[e.end], e.end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    a = h*W+w
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        es[a].append(Edge(b, 0))
                    else:
                        es[a].append(Edge(b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

import heapq

INF = 10 ** 10

class Edge():
    def __init__(self, end, cost):
        self.end = end
        self.cost = cost

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for e in G[v]:
            if dist[e.end] > dist[v] + e.cost:
                dist[e.end] = dist[v] + e.cost
                heapq.heappush(h, (dist[e.end], e.end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = {i:[] for i in range(N)}

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    a = h*W+w
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        es[a].append(Edge(b, 0))
                    else:
                        es[a].append(Edge(b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

import heapq

INF = 10 ** 10

class Edge():
    def __init__(self, end, cost):
        self.end = end
        self.cost = cost

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for e in G[v]:
            if dist[e.end] > dist[v] + e.cost:
                dist[e.end] = dist[v] + e.cost
                heapq.heappush(h, (dist[e.end], e.end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = [[] for i in range(N)]

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    a = h*W+w
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        es[a].append(Edge(b, 0))
                    else:
                        es[a].append(Edge(b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

import heapq

INF = 10 ** 10

class Edge():
    def __init__(self, start, end, cost):
        self.start = start
        self.end = end
        self.cost = cost
    def __str__(self):
        return 'Edge: {} -> {}, cost {}'.format(self.start, self.end, self.cost)

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for e in G[v]:
            if dist[e.end] > dist[v] + e.cost:
                dist[e.end] = dist[v] + e.cost
                heapq.heappush(h, (dist[e.end], e.end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = [[] for i in range(N)]

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    a = h*W+w
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        es[a].append(Edge(a, b, 0))
                    else:
                        es[a].append(Edge(a, b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

h, w = map(int, input().split())
ch, cw = map(int, input().split())
gh, gw = map(int, input().split())

s = []
for i in range(h):
   s.append(input().rstrip('\n'))

INF = 10 ** 10
d = [INF] * (h*w)

stack = deque([[ch-1, cw-1, 0]])
stack_append = stack.append
stack_popleft = stack.popleft

nex = []
for i in range(-2, 3):
    for j in range(-2, 3):
        if (i, j) in [(-1,0),(1,0),(0,-1),(0,1),(0,0)]:
            continue
        else:
            nex.append((i,j))

while stack:
    curh, curw, cnt = stack_popleft()
    f = 0
    if d[curh * w + curw] <= cnt:
        continue
    else:
        d[curh * w + curw] = cnt
    for dh, dw in ((-1,0), (1,0), (0,1), (0,-1)):
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w:
            if s[nh][nw] == '.':
                stack_append([nh, nw, cnt])
            else:
                f = 1
    if f:
        for dh, dw in nex:
            nh = curh + dh
            nw = curw + dw
            if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.' and  d[nh * w + nw] > cnt:
                stack_append([nh, nw, cnt+1])

# for item in d:
#     print(item)
gh -= 1
gw -= 1

if d[gh*w + gw] == INF:
    print(-1)
else:
    print(d[gh*w + gw])


Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

Buggy python submission (verdict: Runtime Error):
import sys
input = sys.stdin.readline
from collections import deque

h, w = map(int, input().split())
ch, cw = map(int, input().split())
gh, gw = map(int, input().split())

s = []
for i in range(h):
   s.append(input().rstrip('\n'))

INF = 10 ** 10
d = [INF] * (h*w)

stack = deque([[ch-1, cw-1, 0]])
stack_append = stack.append
stack_popleft = stack.popleft

nex = []
for i in range(-2, 3):
    for j in range(-2, 3):
        if (i, j) in [(-1,0),(1,0),(0,-1),(0,1),(0,0)]:
            continue
        else:
            nex.append((i,j))

while stack:
    curh, curw, cnt = stack_popleft()
    f = 0
    if d[curh * w + curw] <= cnt:
        continue
    else:
        d[curh * w + curw] = cnt
    for dh, dw in ((-1,0), (1,0), (0,1), (0,-1)):
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.' and d[nh * w + nw] > cnt:
            stack_append([nh, nw, cnt])
        if s[nh][nw] == '#':
            f = 1
    if f:
        for dh, dw in nex:
            nh = curh + dh
            nw = curw + dw
            if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.' and  d[nh * w + nw] > cnt:
                stack_append([nh, nw, cnt+1])

# for item in d:
#     print(item)
gh -= 1
gw -= 1

if d[gh*w + gw] == INF:
    print(-1)
else:
    print(d[gh*w + gw])


Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

h, w = map(int, input().split())
ch, cw = map(int, input().split())
gh, gw = map(int, input().split())

s = []
for i in range(h):
   s.append(input().rstrip('\n'))

INF = 10 ** 10
d = [INF] * (h*w)

stack = deque([[ch-1, cw-1, 0]])
stack_append = stack.append
stack_popleft = stack.popleft

nex = []
for i in range(-2, 3):
    for j in range(-2, 3):
        if (i, j) in [(-1,0),(1,0),(0,-1),(0,1),(0,0)]:
            continue
        else:
            nex.append((i,j))

while stack:
    curh, curw, cnt = stack_popleft()
    if d[curh * w + curw] <= cnt:
        continue
    else:
        d[curh * w + curw] = cnt
    for dh, dw in ((-1,0), (1,0), (0,1), (0,-1)):
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.' and d[nh * w + nw] > cnt:
            stack_append([nh, nw, cnt])
    for dh, dw in nex:
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.' and  d[nh * w + nw] > cnt:
            stack_append([nh, nw, cnt+1])

# for item in d:
#     print(item)
gh -= 1
gw -= 1

if d[gh*w + gw] == INF:
    print(-1)
else:
    print(d[gh*w + gw])

Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

h, w = map(int, input().split())
ch, cw = map(int, input().split())
gh, gw = map(int, input().split())

s = []
for i in range(h):
   s.append(input().rstrip('\n'))

INF = 10 ** 10
d = [INF] * (h*w)

stack = deque([[ch-1, cw-1, 0]])
stack_append = stack.append
stack_popleft = stack.popleft

nex = []
for i in range(-2, 3):
    for j in range(-2, 3):
        if (i, j) in [(-1,0),(1,0),(0,-1),(0,1),(0,0)]:
            continue
        else:
            nex.append((i,j))

while stack:
    curh, curw, cnt = stack_popleft()
    if d[curh * w + curw] <= cnt:
        continue
    else:
        d[curh * w + curw] = cnt
    for dh, dw in ((-1,0), (1,0), (0,1), (0,-1)):
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.':
            stack_append([nh, nw, cnt])
    for dh, dw in nex:
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.':
            stack_append([nh, nw, cnt+1])

# for item in d:
#     print(item)
gh -= 1
gw -= 1

if d[gh*w + gw] == INF:
    print(-1)
else:
    print(d[gh*w + gw])


Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

h, w = map(int, input().split())
ch, cw = map(int, input().split())
gh, gw = map(int, input().split())

s = []
for i in range(h):
   s.append(input().rstrip('\n'))

INF = 10 ** 10
d = [INF] * (h*w)

stack = deque([[ch-1, cw-1, 0]])
stack_append = stack.append
stack_popleft = stack.popleft

nex = []
for i in range(-2, 3):
    for j in range(-2, 3):
        if (i, j) in [(-1,0),(1,0),(0,-1),(0,1),(0,0)]:
            continue
        else:
            nex.append((i,j))

while stack:
    curh, curw, cnt = stack_popleft()
    if d[curh * w + curw] <= cnt:
        continue
    else:
        d[curh * w + curw] = cnt
    for dh, dw in ((-1,0), (1,0), (0,1), (0,-1)):
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.':
            stack_append([nh, nw, cnt])
    for dh, dw in nex:
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.':
            stack_append([nh, nw, cnt+1])

# for item in d:
#     print(item)
gh -= 1
gw -= 1

if d[gh*w + gw] == INF:
    print(-1)
else:
    print(d[gh*w + gw])

Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

h, w = map(int, input().split())
ch, cw = map(int, input().split())
gh, gw = map(int, input().split())

s = ''
for i in range(h):
   s =  s + input().rstrip('\n')

INF = 10 ** 10
d = [INF] * (h*w)

stack = deque([[ch-1, cw-1, 0]])
stack_append = stack.append
stack_popleft = stack.popleft

nex = []
for i in range(-2, 3):
    for j in range(-2, 3):
        if (i, j) in [(-1,0),(1,0),(0,-1),(0,1),(0,0)]:
            continue
        else:
            nex.append((i,j))

while stack:
    curh, curw, cnt = stack_popleft()
    if d[curh * w + curw] <= cnt:
        continue
    else:
        d[curh * w + curw] = cnt
    for dh, dw in ((-1,0), (1,0), (0,1), (0,-1)):
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh * w + nw] == '.':
            stack_append([nh, nw, cnt])
    for dh, dw in nex:
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh * w + nw] == '.':
            stack_append([nh, nw, cnt+1])

# for item in d:
#     print(item)
gh -= 1
gw -= 1

if d[gh*w + gw] == INF:
    print(-1)
else:
    print(d[gh*w + gw])

Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

h, w = map(int, input().split())
ch, cw = map(int, input().split())
gh, gw = map(int, input().split())

s = []
for i in range(h):
    s.extend(input().rstrip('\n'))

INF = 10 ** 10
d = [INF] * (h*w)

stack = deque([[ch-1, cw-1, 0]])
stack_append = stack.append
stack_popleft = stack.popleft


while stack:
    curh, curw, cnt = stack_popleft()
    if d[curh * w + curw] <= cnt:
        continue
    else:
        d[curh * w + curw] = cnt
    for dh, dw in ((-1,0), (1,0), (0,1), (0,-1)):
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh * w + nw] == '.':
            stack_append([nh, nw, cnt])
    for nh in range(curh-2, curh+3):
        if nh >= 0 and nh < h:
            for nw in range(curw-2,curw+3):
                if nw >= 0 and nw < w and s[nh * w + nw] == '.':
                     stack_append([nh, nw, cnt+1])

# for item in d:
#     print(item)
gh -= 1
gw -= 1

if d[gh*w + gw] == INF:
    print(-1)
else:
    print(d[gh*w + gw])

Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

h, w = map(int, input().split())
ch, cw = map(int, input().split())
gh, gw = map(int, input().split())

s = []
for i in range(h):
    s.extend(input().rstrip('\n'))

d = [10 ** 18 for j in range(h*w)]

stack = deque([[ch-1, cw-1, 0]])
stack_append = stack.append
stack_popleft = stack.popleft


while stack:
    curh, curw, cnt = stack_popleft()
    if d[curh * w + curw] <= cnt:
        continue
    else:
        d[curh * w + curw] = cnt
    for dh, dw in ((-1,0), (1,0), (0,1), (0,-1)):
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh * w + nw] == '.':
            stack_append([nh, nw, cnt])
    for nh in range(curh-2, curh+3):
        if nh >= 0 and nh < h:
            for nw in range(curw-2,curw+3):
                if nw >= 0 and nw < w and s[nh * w + nw] == '.':
                     stack_append([nh, nw, cnt+1])

# for item in d:
#     print(item)
gh -= 1
gw -= 1

if d[gh*w + gw] == 10 ** 18:
    print(-1)
else:
    print(d[gh*w + gw])

Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

h, w = map(int, input().split())
ch, cw = map(int, input().split())
gh, gw = map(int, input().split())

s = []
for i in range(h):
    s.append(input().rstrip('\n'))

d = [10 ** 18 for j in range(h*w)]

stack = deque([[ch-1, cw-1, 0]])

while stack:
    curh, curw, cnt = stack.popleft()
    if d[curh * w + curw] <= cnt:
        continue
    else:
        d[curh * w + curw] = cnt
    for dh, dw in ((-1,0), (1,0), (0,1), (0,-1)):
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.':
            stack.append([nh, nw, cnt])
    for nh in range(curh-2, curh+3):
        if nh >= 0 and nh < h:
            for nw in range(curw-2,curw+3):
                if nw >= 0 and nw < w and s[nh][nw] == '.':
                     stack.append([nh, nw, cnt+1])

# for item in d:
#     print(item)
gh -= 1
gw -= 1

if d[gh*w + gw] == 10 ** 18:
    print(-1)
else:
    print(d[gh*w + gw])

Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])

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

h, w = map(int, input().split())
ch, cw = map(int, input().split())
gh, gw = map(int, input().split())

s = []
for i in range(h):
    s.append(input().rstrip('\n'))

d = [[10 ** 18 for i in range(w)] for j in range(h)]

stack = deque([[ch-1, cw-1, 0]])

while stack:
    curh, curw, cnt = stack.popleft()
    if d[curh][curw] <= cnt:
        continue
    else:
        d[curh][curw] = cnt
    for dh, dw in ((-1,0), (1,0), (0,1), (0,-1)):
        nh = curh + dh
        nw = curw + dw
        if nh >= 0 and nh < h and nw >= 0 and nw < w and s[nh][nw] == '.':
            stack.append([nh, nw, cnt])
    for nh in range(curh-2, curh+3):
        if nh >= 0 and nh < h:
            for nw in range(curw-2,curw+3):
                if nw >= 0 and nw < w and s[nh][nw] == '.':
                     stack.append([nh, nw, cnt+1])

# for item in d:
#     print(item)

if d[gh-1][gw-1] == 10 ** 18:
    print(-1)
else:
    print(d[gh-1][gw-1])

Fixed submission:
import sys
input = sys.stdin.readline

import heapq

INF = 10 ** 10

def dijkstra(n, G, s):
    dist = [INF] * n
    dist[s] = 0
    h = []
    heapq.heappush(h, (0, s))

    while h:
        # 使っていない頂点のうち、現時点で最も距離の近いものを選びvとする
        d, v = heapq.heappop(h)
        if dist[v] < d:
            continue
        # vから到達可能な頂点について、距離が短くなれば更新
        for end, cost in G[v]:
            if dist[end] > dist[v] + cost:
                dist[end] = dist[v] + cost
                heapq.heappush(h, (dist[end], end))
    return dist


H, W = map(int, input().split())
N = H * W
ch, cw = map(lambda x:int(x)-1, input().split())
gh, gw = map(lambda x:int(x)-1, input().split())

s = []
es = tuple([] for i in range(N))

for h in range(H):
   s.append(input().rstrip('\n'))

for h in range(H):
    for w in range(W):
        if s[h][w] != '.':
            continue
        a = h*W+w
        esappend = es[a].append
        for dh in (-2, -1, 0, 1, 2):
            for dw in (-2, -1, 0, 1, 2):
                if dh == 0 and dw == 0:
                    continue
                nh = h + dh
                nw = w + dw
                if 0 <= nh and nh < H and 0 <= nw and nw < W and s[nh][nw] == '.':
                    b = nh*W+nw
                    if (dh, dw) in [(-1,0),(1,0),(0,-1),(0,1)]:
                        esappend((b, 0))
                    else:
                        esappend((b, 1))

dist = dijkstra(N, es, ch*W+cw)
if dist[gh*W+gw] == INF:
    print(-1)
else:
    print(dist[gh*W+gw])