Buggy python submission (verdict: Runtime Error):
h, w = map(int, input().split())
Ch, Cw = map(int, input().split())
Dh, Dw = map(int, input().split())
a = [[] for i in range(h)]
for i in range(h):
    a[i] = input()

d = [[0, -1], [1, 0], [0, 1], [-1, 0]]
ans = 0
stock 
root_list = []
def dfs(start_h, start_w, r2):
    a[start_h][start_w] = '#'
    if (start_h==Dh) && (start_w==Dw):
        return True
    for i in range(-2, 3):
        for j in range(-2, 3):
            if ((i<-1)||(i>1)) && ((j<-1)||(j>1)):
                s_h = start_h+i; s_w = start_w+j
                if(0<=(start_h+i)<h) && (0<=(start_w+j)<w):
                    if a[s_h][s_w]=='.':
                        root_list.append([s_h, s_w, ans])
    for i in d:
        next_h=start_h+i[0]; next_w=start_w+i[1]
        if(0<=next_h<h) && (0<=next_w<w) && (a[next_h][next_w]=='.')):
            dfs(next_h, next_w, root_list)
def main():
    if(dfs(Ch, Cw, 0)):
        print(0)
        return
    while root_list:
        r0 = root_list[0][0]; r1 = root_list[0][1]; r2=root_list[0][2]+1
        root_list.pop(0)
        if a[r0][r1] == '.':
            root_list[2]
            if dfs(r0, r1, r2):
                print(r2)
                break
    print(-1)
main()

Fixed submission:
from collections import deque

def inc(y, x):
	return 0 <= y < H and 0 <= x < W

H, W = map(int, input().split())
Sy, Sx = map(int, input().split())
Gy, Gx = map(int, input().split())
"""
a = [[] for i in range(h)]
for i in range(h):
    a[i] = input()
"""
a = [input() for i in range(H)]

DH = [1, 0, -1, 0]
DW = [0, 1, 0, -1]

#同じ大きさの行列を作って最短路をメモする発想がなかった
visit = [[1e8 for i in range(W)] for j in range(H)]
visit[Sy-1][Sx-1]=0 #sy-1, sx-1に注意
deq = deque([(Sy-1, Sx-1)])

while deq:
    h, w = deq.pop()
    for dh, dw in zip(DH, DW):
        x = w+dw; y=h+dh
        if inc(y, x)==False or a[y][x]=='#':
            continue
        if visit[y][x] > visit[h][w]:
            visit[y][x] = visit[h][w]
            deq.append((y,x))
    for dh in range(-2, 3):
        for dw in range(-2, 3):
            if inc(h+dh, w+dw)==False or a[h+dh][w+dw]=='#':
                continue
            if visit[h+dh][w+dw] > visit[h][w]+1: 
                visit[h+dh][w+dw] = visit[h][w]+1
                deq.appendleft((h+dh, w+dw))
if visit[Gy-1][Gx-1] == 1e8:
    print(-1)
else:
    print(visit[Gy-1][Gx-1])

Buggy python submission (verdict: Runtime Error):
h, w = map(int, input().split())
Ch, Cw = map(int, input().split())
Dh, Dw = map(int, input().split())
a = [[] for i in range(h)]
for i in range(h):
    a[i] = input()

d = [[0, -1], [1, 0], [0, 1], [-1, 0]]
ans = 0
stock 
root_list = []
def dfs(start_h, start_w, r2):
    a[start_h][start_w] = '#'
    if (start_h==Dh) && (start_w==Dw):
        return True
    for i in range(-2, 3):
        for j in range(-2, 3):
            if ((i<-1)||(i>1)) && ((j<-1)||(j>1)):
                s_h = start_h+i; s_w = start_w+j
                if(0<=(start_h+i)<h) && (0<=(start_w+j)<w):
                    if a[s_h][s_w]=='.':
                        root_list.append([s_h, s_w, ans])
    for i in d:
        next_h=start_h+i[0]; next_w=start_w+i[1]
        if(0<=next_h<h) && (0<=next_w<w) && (a[next_h][next_w]=='.')):
            dfs(next_h, next_w, root_list)
def main():
    if(dfs(Ch, Cw, 0)):
        print(0)
        return
    while root_list:
        r0 = root_list[0][0]; r1 = root_list[0][1]; r2=root_list[0][2]+1
        root_list.pop(0)
        if a[r0][r1] == '.':
            root_list[2]
            if dfs(r0, r1, r2):
                print(r2)
                break
    print(-1)

Fixed submission:
from collections import deque

def inc(y, x):
	return 0 <= y < H and 0 <= x < W

H, W = map(int, input().split())
Sy, Sx = map(int, input().split())
Gy, Gx = map(int, input().split())
"""
a = [[] for i in range(h)]
for i in range(h):
    a[i] = input()
"""
a = [input() for i in range(H)]

DH = [1, 0, -1, 0]
DW = [0, 1, 0, -1]

#同じ大きさの行列を作って最短路をメモする発想がなかった
visit = [[1e8 for i in range(W)] for j in range(H)]
visit[Sy-1][Sx-1]=0 #sy-1, sx-1に注意
deq = deque([(Sy-1, Sx-1)])

while deq:
    h, w = deq.pop()
    for dh, dw in zip(DH, DW):
        x = w+dw; y=h+dh
        if inc(y, x)==False or a[y][x]=='#':
            continue
        if visit[y][x] > visit[h][w]:
            visit[y][x] = visit[h][w]
            deq.append((y,x))
    for dh in range(-2, 3):
        for dw in range(-2, 3):
            if inc(h+dh, w+dw)==False or a[h+dh][w+dw]=='#':
                continue
            if visit[h+dh][w+dw] > visit[h][w]+1: 
                visit[h+dh][w+dw] = visit[h][w]+1
                deq.appendleft((h+dh, w+dw))
if visit[Gy-1][Gx-1] == 1e8:
    print(-1)
else:
    print(visit[Gy-1][Gx-1])