Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
INF = 10**7
import sys
input = sys.stdin.readline
from collections import*

def bfs(sx, sy, gx, gy, c):
    q = deque([(sx, sy)])
    dist = [[INF] * W for _ in range(H)]
    dist[sx][sy] = 0
    
    while q:
        x, y = q.popleft()
        if (x, y) == (gx, gy): return dist[gx][gy]
        for nx, ny in [(x-1, y), (x+1, y), (x, y-1), (x, y+1)]:
            if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                if c[nx][ny] == ".":
                    dist[nx][ny] = dist[x][y]
                    q.appendleft((nx, ny))
        for nx in range(x-2, x+3):
            for ny in range(y-2, y+3):
                if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                    if c[nx][ny] == ".":
                        dist[nx][ny] = dist[x][y] + 1
                        q.append((nx, ny)) 
    return -1
H, W = map(int, input().split())

cx, cy = map(int, input().split())
dx, dy = map(int, input().split())
ans = bfs(cx - 1, cy - 1, dx - 1, dy - 1, [input()[:-1] for _ in range(H)])
print(ans if ans != INF else -1)


Fixed submission:
#!/usr/bin/env python3
INF = 10**7
import sys
input = sys.stdin.readline
from collections import*

def bfs():
    q = deque([(sx, sy)])
    dist = [[INF] * W for _ in range(H)]
    dist[sx][sy] = 0
    
    while q:
        x, y = q.popleft()
        b = dist[x][y]
        if (x, y) == (gx, gy):
            return b
        for dx, dy in [(1, 0), (-1, 0), (0, 1), (0, -1)]:
            nx, ny = x + dx, y + dy
            if 0 <= nx < H and 0 <= ny < W and dist[nx][ny] > b and c[nx][ny] == ".":
                dist[nx][ny] = b
                q.appendleft((nx, ny))
        B = b + 1
        for dx in range(-2, 3):
            for dy in range(-2, 3):
                nx, ny = x + dx, y + dy
                if 0 <= nx < H and 0 <= ny < W and dist[nx][ny] > B and c[nx][ny] == ".":
                    dist[nx][ny] = B
                    q.append((nx, ny)) 
    return -1

H, W = map(int, input().split())
cx, cy = map(int, input().split())
dx, dy = map(int, input().split())
sx, sy, gx, gy = cx - 1, cy - 1, dx - 1, dy - 1
c = [input()[:-1] for _ in range(H)]
ans = bfs()
print(ans if ans != INF else -1)

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
INF = 10**7
import sys
input = sys.stdin.readline
from collections import*

def bfs():
    q = deque([(sx, sy)])
    dist = [[INF]*W for _ in range(H)]
    dist[sx][sy] = 0
    
    while q:
        x, y = q.popleft()
        b = dist[x][y]
        if (x, y) == (gx, gy): return dist[gx][gy]
        for nx, ny in [(x-1, y), (x+1, y), (x, y-1), (x, y+1)]:
            if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                if c[nx][ny] == ".":
                    dist[nx][ny] = dist[x][y]
                    q.appendleft((nx, ny))
        for nx in range(x-2, x+3):
            for ny in range(y-2, y+3):
                if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                    if c[nx][ny] == ".":
                        dist[nx][ny] = dist[x][y] + 1
                        q.append((nx, ny)) 
    return -1
H, W = map(int, input().split())

cx, cy = map(int, input().split()); sx, sy = cx - 1, cy - 1
dx, dy = map(int, input().split()); gx, gy = dx - 1, dy - 1
c = [input()[:-1] for _ in range(H)]
ans = bfs()
print(ans if ans != INF else -1)


Fixed submission:
#!/usr/bin/env python3
INF = 10**7
import sys
input = sys.stdin.readline
from collections import*

def bfs():
    q = deque([(sx, sy)])
    dist = [[INF] * W for _ in range(H)]
    dist[sx][sy] = 0
    
    while q:
        x, y = q.popleft()
        b = dist[x][y]
        if (x, y) == (gx, gy):
            return b
        for dx, dy in [(1, 0), (-1, 0), (0, 1), (0, -1)]:
            nx, ny = x + dx, y + dy
            if 0 <= nx < H and 0 <= ny < W and dist[nx][ny] > b and c[nx][ny] == ".":
                dist[nx][ny] = b
                q.appendleft((nx, ny))
        B = b + 1
        for dx in range(-2, 3):
            for dy in range(-2, 3):
                nx, ny = x + dx, y + dy
                if 0 <= nx < H and 0 <= ny < W and dist[nx][ny] > B and c[nx][ny] == ".":
                    dist[nx][ny] = B
                    q.append((nx, ny)) 
    return -1

H, W = map(int, input().split())
cx, cy = map(int, input().split())
dx, dy = map(int, input().split())
sx, sy, gx, gy = cx - 1, cy - 1, dx - 1, dy - 1
c = [input()[:-1] for _ in range(H)]
ans = bfs()
print(ans if ans != INF else -1)

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
INF = float("inf")
import sys
input = sys.stdin.readline
from collections import*

def bfs():
    q = deque([(sx, sy)])
    dist = [[INF]*W for _ in range(H)]
    dist[sx][sy] = 0
    
    while q:
        x, y = q.popleft()
        if (x, y) == (gx, gy): return dist[gx][gy]
        for nx, ny in [(x-1, y), (x+1, y), (x, y-1), (x, y+1)]:
            if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                if c[nx][ny] == ".":
                    dist[nx][ny] = dist[x][y]
                    q.appendleft((nx, ny))
        for nx in range(x-2, x+3):
            for ny in range(y-2, y+3):
                if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                    if c[nx][ny] == ".":
                        dist[nx][ny] = dist[x][y] + 1
                        q.append((nx, ny)) 
    return -1
H, W = map(int, input().split())

cx, cy = map(int, input().split()); sx, sy = cx - 1, cy - 1
dx, dy = map(int, input().split()); gx, gy = dx - 1, dy - 1
c = [input()[:-1] for _ in range(H)]
ans = bfs()
print(ans if ans != INF else -1)


Fixed submission:
#!/usr/bin/env python3
INF = 10**7
import sys
input = sys.stdin.readline
from collections import*

def bfs():
    q = deque([(sx, sy)])
    dist = [[INF] * W for _ in range(H)]
    dist[sx][sy] = 0
    
    while q:
        x, y = q.popleft()
        b = dist[x][y]
        if (x, y) == (gx, gy):
            return b
        for dx, dy in [(1, 0), (-1, 0), (0, 1), (0, -1)]:
            nx, ny = x + dx, y + dy
            if 0 <= nx < H and 0 <= ny < W and dist[nx][ny] > b and c[nx][ny] == ".":
                dist[nx][ny] = b
                q.appendleft((nx, ny))
        B = b + 1
        for dx in range(-2, 3):
            for dy in range(-2, 3):
                nx, ny = x + dx, y + dy
                if 0 <= nx < H and 0 <= ny < W and dist[nx][ny] > B and c[nx][ny] == ".":
                    dist[nx][ny] = B
                    q.append((nx, ny)) 
    return -1

H, W = map(int, input().split())
cx, cy = map(int, input().split())
dx, dy = map(int, input().split())
sx, sy, gx, gy = cx - 1, cy - 1, dx - 1, dy - 1
c = [input()[:-1] for _ in range(H)]
ans = bfs()
print(ans if ans != INF else -1)

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
# 方針は分かったのでヨシ！バチャやって実装力つけたい
INF = float("inf")
import sys
input = sys.stdin.readline
from collections import*

def bfs():
    q = deque([(sx, sy)])
    dist = [[INF]*W for _ in range(H)]
    dist[sx][sy] = 0
    
    while q:
        x, y = q.popleft()
        if (x, y) == (gx, gy): return dist[gx][gy]
        for nx, ny in [(x-1, y), (x+1, y), (x, y-1), (x, y+1)]:
            if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                if c[nx][ny] == ".":
                    dist[nx][ny] = dist[x][y]
                    q.appendleft((nx, ny))
        for nx in range(x-2, x+3):
            for ny in range(y-2, y+3):
                if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                    if c[nx][ny] == ".":
                        dist[nx][ny] = dist[x][y] + 1
                        q.append((nx, ny)) 
    return -1
H, W = map(int, input().split())

cx, cy = map(int, input().split()); sx, sy = cx - 1, cy - 1
dx, dy = map(int, input().split()); gx, gy = dx - 1, dy - 1
c = [input()[:-1] for _ in range(H)]
ans = bfs()
print(ans if ans != INF else -1)


Fixed submission:
#!/usr/bin/env python3
INF = 10**7
import sys
input = sys.stdin.readline
from collections import*

def bfs():
    q = deque([(sx, sy)])
    dist = [[INF] * W for _ in range(H)]
    dist[sx][sy] = 0
    
    while q:
        x, y = q.popleft()
        b = dist[x][y]
        if (x, y) == (gx, gy):
            return b
        for dx, dy in [(1, 0), (-1, 0), (0, 1), (0, -1)]:
            nx, ny = x + dx, y + dy
            if 0 <= nx < H and 0 <= ny < W and dist[nx][ny] > b and c[nx][ny] == ".":
                dist[nx][ny] = b
                q.appendleft((nx, ny))
        B = b + 1
        for dx in range(-2, 3):
            for dy in range(-2, 3):
                nx, ny = x + dx, y + dy
                if 0 <= nx < H and 0 <= ny < W and dist[nx][ny] > B and c[nx][ny] == ".":
                    dist[nx][ny] = B
                    q.append((nx, ny)) 
    return -1

H, W = map(int, input().split())
cx, cy = map(int, input().split())
dx, dy = map(int, input().split())
sx, sy, gx, gy = cx - 1, cy - 1, dx - 1, dy - 1
c = [input()[:-1] for _ in range(H)]
ans = bfs()
print(ans if ans != INF else -1)

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
INF = float("inf")
import sys
input = sys.stdin.readline
from collections import*

def bfs():
    q = deque([(sx, sy)])
    dist = [[INF]*W for _ in range(H)]
    dist[sx][sy] = 0
    
    while q:
        x, y = q.popleft()
        if (x, y) == (gx, gy): return dist[gx][gy]
        for nx, ny in [(x-1, y), (x+1, y), (x, y-1), (x, y+1)]:
            if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                if c[nx][ny] == ".":
                    dist[nx][ny] = dist[x][y]
                    q.appendleft((nx, ny))
        for nx, ny in [(x-1, y-1), (x-1, y+1), (x+1, y+1), (x+1, y-1)]:
            if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                if c[nx][ny] == ".":
                    dist[nx][ny] = dist[x][y] + 1
                    q.append((nx, ny))
        for nx in range(x-2, x+3):
            for ny in [y+2, y-2]:
                if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                    if c[nx][ny] == ".":
                        dist[nx][ny] = dist[x][y] + 1
                        q.append((nx, ny))
        for nx in [x+2, x-2]:
            for ny in range(y-1, y+2):
                if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                    if c[nx][ny] == ".":
                        dist[nx][ny] = dist[x][y] + 1
                        q.append((nx, ny))            
    return dist[gx][gy]

H, W = map(int, input().split())

cx, cy = map(int, input().split()); sx, sy = cx - 1, cy - 1
dx, dy = map(int, input().split()); gx, gy = dx - 1, dy - 1
c = [input()[:-1] for _ in range(H)]
ans = bfs()
print(ans if ans != INF else -1)


Fixed submission:
#!/usr/bin/env python3
INF = 10**7
import sys
input = sys.stdin.readline
from collections import*

def bfs():
    q = deque([(sx, sy)])
    dist = [[INF] * W for _ in range(H)]
    dist[sx][sy] = 0
    
    while q:
        x, y = q.popleft()
        b = dist[x][y]
        if (x, y) == (gx, gy):
            return b
        for dx, dy in [(1, 0), (-1, 0), (0, 1), (0, -1)]:
            nx, ny = x + dx, y + dy
            if 0 <= nx < H and 0 <= ny < W and dist[nx][ny] > b and c[nx][ny] == ".":
                dist[nx][ny] = b
                q.appendleft((nx, ny))
        B = b + 1
        for dx in range(-2, 3):
            for dy in range(-2, 3):
                nx, ny = x + dx, y + dy
                if 0 <= nx < H and 0 <= ny < W and dist[nx][ny] > B and c[nx][ny] == ".":
                    dist[nx][ny] = B
                    q.append((nx, ny)) 
    return -1

H, W = map(int, input().split())
cx, cy = map(int, input().split())
dx, dy = map(int, input().split())
sx, sy, gx, gy = cx - 1, cy - 1, dx - 1, dy - 1
c = [input()[:-1] for _ in range(H)]
ans = bfs()
print(ans if ans != INF else -1)

Buggy python submission (verdict: Time Limit Exceeded):
#!/usr/bin/env python3
# 方針は分かったのでヨシ！ (dist[nx][ny] > dist[x][y] を忘れてた　後コードきたねえ)
INF = float("inf")
import sys
input = sys.stdin.readline
from collections import*

def bfs():
    q = deque([(sx, sy)])
    dist = [[INF]*W for _ in range(H)]
    dist[sx][sy] = 0
    
    while q:
        x, y = q.popleft()
        for nx, ny in [(x-1, y), (x+1, y), (x, y-1), (x, y+1)]:
            if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                if c[nx][ny] == ".":
                    dist[nx][ny] = dist[x][y]
                    q.appendleft((nx, ny))
        for nx, ny in [(x-1, y-1), (x-1, y+1), (x+1, y+1), (x+1, y-1)]:
            if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                if c[nx][ny] == ".":
                    dist[nx][ny] = dist[x][y] + 1
                    q.append((nx, ny))
        for nx in range(x-2, x+3):
            for ny in [y+2, y-2]:
                if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                    if c[nx][ny] == ".":
                        dist[nx][ny] = dist[x][y] + 1
                        q.append((nx, ny))
        for nx in [x+2, x-2]:
            for ny in range(y-1, y+2):
                if 0<=nx<H and 0<=ny<W and dist[nx][ny] > dist[x][y]:
                    if c[nx][ny] == ".":
                        dist[nx][ny] = dist[x][y] + 1
                        q.append((nx, ny))            
    return dist[gx][gy]

H, W = map(int, input().split())

cx, cy = map(int, input().split()); sx, sy = cx - 1, cy - 1
dx, dy = map(int, input().split()); gx, gy = dx - 1, dy - 1
c = [input()[:-1] for _ in range(H)]
ans = bfs()
print(ans if ans != INF else -1)

Fixed submission:
#!/usr/bin/env python3
INF = 10**7
import sys
input = sys.stdin.readline
from collections import*

def bfs():
    q = deque([(sx, sy)])
    dist = [[INF] * W for _ in range(H)]
    dist[sx][sy] = 0
    
    while q:
        x, y = q.popleft()
        b = dist[x][y]
        if (x, y) == (gx, gy):
            return b
        for dx, dy in [(1, 0), (-1, 0), (0, 1), (0, -1)]:
            nx, ny = x + dx, y + dy
            if 0 <= nx < H and 0 <= ny < W and dist[nx][ny] > b and c[nx][ny] == ".":
                dist[nx][ny] = b
                q.appendleft((nx, ny))
        B = b + 1
        for dx in range(-2, 3):
            for dy in range(-2, 3):
                nx, ny = x + dx, y + dy
                if 0 <= nx < H and 0 <= ny < W and dist[nx][ny] > B and c[nx][ny] == ".":
                    dist[nx][ny] = B
                    q.append((nx, ny)) 
    return -1

H, W = map(int, input().split())
cx, cy = map(int, input().split())
dx, dy = map(int, input().split())
sx, sy, gx, gy = cx - 1, cy - 1, dx - 1, dy - 1
c = [input()[:-1] for _ in range(H)]
ans = bfs()
print(ans if ans != INF else -1)