Problem:
Score : 400 points

Problem Statement

A maze is composed of a grid of H \times W squares - H vertical, W horizontal.

The square at the i-th row from the top and the j-th column from the left - (i,j) - is a wall if S_{ij} is # and a road if S_{ij} is ..

There is a magician in (C_h,C_w). He can do the following two kinds of moves:

Move A: Walk to a road square that is vertically or horizontally adjacent to the square he is currently in.

Move B: Use magic to warp himself to a road square in the 5\times 5 area centered at the square he is currently in.

In either case, he cannot go out of the maze.

At least how many times does he need to use the magic to reach (D_h, D_w)?

Constraints

1 \leq H,W \leq 10^3

1 \leq C_h,D_h \leq H

1 \leq C_w,D_w \leq W

S_{ij} is # or ..

S_{C_h C_w} and S_{D_h D_w} are ..

(C_h,C_w) \neq (D_h,D_w)

Input

Input is given from Standard Input in the following format:

H W
C_h C_w
D_h D_w
S_{11}\ldots S_{1W}
\vdots
S_{H1}\ldots S_{HW}

Output

Print the minimum number of times the magician needs to use the magic. If he cannot reach (D_h,D_w), print -1 instead.

Sample Input 1

4 4
1 1
4 4
..#.
..#.
.#..
.#..

Sample Output 1

1

For example, by walking to (2,2) and then using the magic to travel to (4,4), just one use of magic is enough.

Note that he cannot walk diagonally.

Sample Input 2

4 4
1 4
4 1
.##.
####
####
.##.

Sample Output 2

-1

He cannot move from there.

Sample Input 3

4 4
2 2
3 3
....
....
....
....

Sample Output 3

0

No use of magic is needed.

Sample Input 4

4 5
1 2
2 5
#.###
####.
#..##
#..##

Sample Output 4

2

Solution in Python (3.8.2) (judge verdict: Wrong Answer)

from collections import deque

H,W = map(int,input().split())
C = list(map(lambda x: int(x) - 1, input().split()))
D = list(map(lambda x: int(x) - 1, input().split()))
# 지도
board = [input() for _ in range(H)]
# 방문 체크
visited = [[False] * W for _ in range(H)]
# bfs를 위한 큐 
dq = deque([[0,C[0],C[1]]])
def dfs(dq):
  while dq:
    cnt, h, w = dq.popleft()
    # 도착점에 도착하면 종료
    if [h,w] == D:
      print(cnt)
      exit()
    visited[h][w] = True
    # 상,하,좌,우 1칸씩 이동
    for move_h, move_w in [[-1,0], [1,0], [0,-1], [0,1]]:
      new_h = h + move_h
      new_w = w + move_w
      # 걸어서 갈 수 있는 경우 앞에서부터 큐에 넣음
      if 0 <= new_h <= H-1 and 0<= new_w <= W-1 and board[new_h][new_w] == '.' and (not visited[new_h][new_w]):
        visited[new_h][new_w] = True
        dq.appendleft([cnt,new_h,new_w])
    # 인접한 5x5 탐색
    for move_h in range(-2,3):
      for move_w in range(-2,3):
        if [move_h, move_w] == [0,0]:
          continue
        new_h = h + move_h
        new_w = w + move_w 
        # 마법을 사용한 경우 뒤에서부터 큐에 넣음
        if 0 <= new_h <= H-1 and 0<= new_w <= W-1 and board[new_h][new_w] == '.' and (not visited[new_h][new_w]):
          visited[new_h][new_w] = True
          dq.append([cnt+1,new_h,new_w])
dfs(dq)
print(-1)