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 C# (.NET Core 3.1.201) (judge verdict: Wrong Answer)

using System;
using System.Collections.Generic;

namespace abc176_d
{
  class Program
  {
    static void Main(string[] args)
    {
      var H = CIn.ReadInt();
      var W = CIn.ReadInt();
      var Ch = CIn.ReadInt() - 1;
      var Cw = CIn.ReadInt() - 1;
      var Dh = CIn.ReadInt() - 1;
      var Dw = CIn.ReadInt() - 1;
      var S = CIn.ReadCharMatrix(H, W);

      var c = new int[H, W];

      for (int i = 0; i < H; i++)
      {
        for (int j = 0; j < W; j++)
        {
          c[i, j] = -1;
          if (S[i, j] == '#') c[i, j] = -2;
        }
      }

      c[Ch, Cw] = 0;

      var set = new HashSet<(int y, int x)>();
      var stack = new Stack<(int y, int x)>();

      stack.Push((Ch, Cw));

      while (stack.Count > 0)
      {
        var (y, x) = stack.Pop();
        set.Add((y, x));

        if (c[y, x] == -1) c[y, x] = 0;

        if (x > 0 && S[y, x - 1] == '.' && !set.Contains((y, x - 1))) stack.Push((y, x - 1));
        if (x < W - 1 && S[y, x + 1] == '.' && !set.Contains((y, x + 1))) stack.Push((y, x + 1));
        if (y > 0 && S[y - 1, x] == '.' && !set.Contains((y - 1, x))) stack.Push((y - 1, x));
        if (y < H - 1 && S[y + 1, x] == '.' && !set.Contains((y + 1, x))) stack.Push((y + 1, x));
      }

      for (int i = 0; c[Dh, Dw] < 0; i++)
      {
        var f = true;
        for (int j = 0; j < H; j++)
        {
          for (int k = 0; k < W; k++)
          {
            if (c[j, k] == i)
            {
              for (int l = -2; l <= 2; l++)
              {
                for (int m = -2; m <= 2; m++)
                {
                  if (0 <= j + l && j + l < H && 0 <= k + m && k + m < W && c[j + l, k + m] == -1)
                  {
                    c[j + l, k + m] = i + 1;
                    f = false;
                  }
                }
              }
            }
          }
        }

        if (f) break;
      }

      Console.WriteLine(c[Dh, Dw]);
    }
  }

  static class CIn
  {
    private static readonly Queue<string> fieldBuffer = new Queue<string>();

    public static string Read()
    {
      if (fieldBuffer.Count == 0)
      {
        foreach (var field in Console.ReadLine().Split())
        {
          fieldBuffer.Enqueue(field);
        }
      }
      return fieldBuffer.Dequeue();
    }

    public static int ReadInt() => int.Parse(Read());
    public static long ReadLong() => long.Parse(Read());
    public static double ReadDouble() => double.Parse(Read());

    public static string[] ReadStringArray(int n)
    {
      var array = new string[n];
      for (var i = 0; i < n; i++)
      {
        array[i] = Read();
      }
      return array;
    }

    public static int[] ReadIntArray(int n)
    {
      var array = new int[n];
      for (var i = 0; i < n; i++)
      {
        array[i] = ReadInt();
      }
      return array;
    }

    public static long[] ReadLongArray(int n)
    {
      var array = new long[n];
      for (var i = 0; i < n; i++)
      {
        array[i] = ReadLong();
      }
      return array;
    }

    public static double[] ReadDoubleArray(int n)
    {
      var array = new double[n];
      for (var i = 0; i < n; i++)
      {
        array[i] = ReadDouble();
      }
      return array;
    }

    public static char[,] ReadCharMatrix(int h, int w)
    {
      var array = new char[h, w];
      for (var i = 0; i < h; i++)
      {
        var l = Console.ReadLine().ToCharArray();
        for (var j = 0; j < w; j++)
        {
          array[i, j] = l[j];
        }
      }
      return array;
    }
  }
}