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;
using System.Text;
using System.Linq;
using System.Numerics;
using System.IO;
using System.Net;
using System.Diagnostics;
using System.Runtime.InteropServices.WindowsRuntime;
using System.Runtime.Remoting;
using System.Runtime.CompilerServices;

namespace Practice
{
    class Program
    {
        static void Main(string[] args)
        {
            var sw = new System.IO.StreamWriter(Console.OpenStandardOutput()) { AutoFlush = false };
            Console.SetOut(sw);
            Solve();

            Console.Out.Flush();
        }
        private const int MOD = 1000000007;
        private const int MAX = 1000001;
        static long[] fac = new long[MAX];
        static long[] finv = new long[MAX];
        static long[] inv = new long[MAX];
        static Dictionary<long, long> primeDic = new Dictionary<long, long>();

        const int kWall = 0;
        const int kGround = 1;
        static char[,] map;// 0壁、
        static Dictionary<Tuple<int, int>, int> _pos_id_table = new Dictionary<Tuple<int, int>, int>();
        static List<Tuple<int, int>>[] _id_poss = new List<Tuple<int, int>>[1000000];
        static string[] s;

        static List<int>[] g = new List<int>[1000000];
        static int[] dist = new int[1000000];
        static HashSet<int>[] gdone = new HashSet<int>[1000000];
        static void Solve()
        {
            var h = Input.NextInt();
            var w = Input.NextInt();
            var ch = Input.NextInt();
            var cw = Input.NextInt();
            var dh = Input.NextInt();
            var dw = Input.NextInt();
            s = new string[h];
            for (int i = 0; i < h; i++)
            {
                s[i] = Input.Next();
            }

            map = new char[h + 4, w + 4];
            for (int i = 0; i < h; i++)
            {
                for (int j = 0; j < w; j++)
                {
                    map[i + 2, j + 2] = s[i][ j] == '#' ? (char)kWall : (char)kGround;
                }
            }
            for (int i = 0; i < _id_poss.Length; i++)
            {
                _id_poss[i] = new List<Tuple<int, int>>();
            }
            for (int i = 0; i < g.Length; i++)
            {
                g[i] = new List<int>();
                gdone[i] = new HashSet<int>();
            }

            int id = 0;
            for (int i = 2; i < h+2; i++)
            {
                for (int j = 2; j < w+2; j++)
                {
                    if(map[i,j] == kWall) { continue; }
                    var v = new Tuple<int, int>(i, j);
                    if (_pos_id_table.ContainsKey(v)) { continue; }

                    
                    bfs0(v, id);
                    id++;
                }
            }
            // グラフ構築
            for (int i = 0; i < _id_poss.Length; i++)
            {
                var vs = _id_poss[i];
                foreach (var v in vs)
                {
                    CheckWarp(v, i);
                }
            }
            int sid = _pos_id_table[new Tuple<int, int>(ch + 1, cw + 1)];
            bfs(sid);
            int eid = _pos_id_table[new Tuple<int, int>(dh + 1, dw + 1)];

            int ans = -1;
            if( sid == eid) { ans = 0; }// 同じエリア
            else
            {
                if( dist[eid] == 0)
                {
                    // たどり着けない
                }
                else
                {
                    ans = dist[eid];
                }
            }
            Console.WriteLine(ans);
        }
        static void bfs0(Tuple<int, int> s , int id)
        {
            var q = new Queue<Tuple<int, int>>();
            q.Enqueue(s);
            if (!_pos_id_table.ContainsKey(s))
            {
                _pos_id_table.Add(s, id);
                _id_poss[id].Add(s);
            }
            while (q.Count > 0)
            {
                var v = q.Dequeue();
                bfs0Internal(v.Item1 + 1, v.Item2, id, q);
                bfs0Internal(v.Item1 - 1, v.Item2, id, q);
                bfs0Internal(v.Item1 , v.Item2 + 1, id, q);
                bfs0Internal(v.Item1 , v.Item2 - 1, id, q);

            }
        }
        static void bfs0Internal(int y, int x, int id, Queue<Tuple<int, int>> q)
        {
            var u = new Tuple<int, int>(y, x);

            if (!_pos_id_table.ContainsKey(u) && map[y, x] == kGround)
            {
                _pos_id_table.Add(u, id);
                _id_poss[id].Add(u);
                q.Enqueue(u);
            }
        }
        static void bfs(int sid)
        {
            var q = new Queue<int>();
            q.Enqueue(sid);
            while(q.Count > 0)
            {
                int v = q.Dequeue();
                var list = g[v];
                foreach (var u in list)
                {
                    if( dist[u] != 0) { continue; }
                    dist[u]++;
                    q.Enqueue(u);
                }
            }

        }
        static void SafeAddPosID(int y, int x, int id)
        {
            var v = new Tuple<int,int>(y,x);
            if(map[y,x ] == kGround && !_pos_id_table.ContainsKey(v))
            {
                _pos_id_table.Add(v, id);
                _id_poss[id].Add(v);
            }
        }
        /// <summary>
        /// ここからワープできる地点を探すぞ
        /// </summary>
        /// <param name="v"></param>
        /// <param name="id"></param>
        static void CheckWarp(Tuple<int, int> v, int id)
        {
            for (int j = -2; j <= 2; j++)
            {
                SafeConnect(v.Item1 + 2, v.Item2+ j, id);
                SafeConnect(v.Item1 - 2, v.Item2 + j, id);
            }
            for (int i = -1; i <= 1; i++)
            {
                SafeConnect(v.Item1 + i, v.Item2 + 2, id);
                SafeConnect(v.Item1 + i, v.Item2 - 2, id);
            }
        }
        static void SafeConnect(int y, int x, int myid)
        {
            var v = new Tuple<int, int>(y, x);
            if (_pos_id_table.ContainsKey(v))
            {
                int id = _pos_id_table[v];
                if(id != myid)
                {
                    if (!gdone[myid].Contains(id))
                    {
                        // 連結
                        g[myid].Add(id);
                        g[id].Add(myid);
                    }
                }
            }
            else
            {

            }
        }


        #region よく使う便利関数

        private static void TrialDivision(long m)
        {
            for (long i = 2; i * i <= m; i++)
            {
                long ex = 0;
                while (m % i == 0)
                {
                    ex++;

                    m /= i;
                }

                if (ex >= 1)
                {
                    primeDic.Add(i, ex);
                }
            }
            if (m >= 2)
            {
                primeDic.Add(m, 1);
            }

            // note まぁ1は違うよね
        }

        private static Dictionary<long, int> Factorize(long n)
        {
            var dic = new Dictionary<long, int>();

            for (long i = 2; i * i <= n; ++i)
            {
                while (n % i == 0)
                {
                    if (!dic.ContainsKey(i))
                    {
                        dic.Add(i, 0);
                    }
                    dic[i]++;
                    n /= i;
                }

            }

            if (n != 1)
            {
                dic.Add(n, 1);
            }
            return dic;
        }
        static void COMinit()
        {
            fac[0] = fac[1] = 1;
            finv[0] = finv[1] = 1;
            inv[1] = 1;
            for (int i = 2; i < MAX; i++)
            {
                fac[i] = fac[i - 1] * i % MOD;
                inv[i] = MOD - inv[MOD % i] * (MOD / i) % MOD;
                finv[i] = finv[i - 1] * inv[i] % MOD;
            }
        }

        // 二項係数計算
        static long COM(long n, long k)
        {
            if (n < k) return 0;
            if (n < 0 || k < 0) return 0;
            return fac[n] * (finv[k] * finv[n - k] % MOD) % MOD;
        }

        static class Input
        {
            static char[] separator = { ' ' };
            public static bool IsEof { get; set; }
            static Queue<string> q { get; set; }

            static Input()
            {
                IsEof = false;
                q = new Queue<string>();
            }

            /// <summary>
            /// 入力予約
            /// </summary>
            /// <param name="items"></param>
            public static void SetText(IEnumerable<string> items)
            {
                foreach (var item in items)
                {
                    SetText(item);
                }
            }

            /// <summary>
            /// 入力予約
            /// </summary>
            /// <param name="s"></param>
            /// <returns></returns>
            public static bool SetText(string s)
            {
                if (s == null) return false;

                foreach (var elem in s.Trim().Split(separator, StringSplitOptions.RemoveEmptyEntries))
                {
                    q.Enqueue(elem);
                }

                return true;
            }

            /// <summary>
            /// 内部queueに入力からの値をsplitして格納する
            /// </summary>
            /// <returns></returns>
            static bool read()
            {
                var s = Console.ReadLine();
                if (s == null) return false;

                foreach (var elem in s.Trim().Split(separator, StringSplitOptions.RemoveEmptyEntries))
                {
                    q.Enqueue(elem);
                }

                if (!q.Any()) return read();

                return true;
            }

            /// <summary>
            /// 次のstringを一つ読み込む
            /// </summary>
            /// <returns></returns>
            public static string Next()
            {
                if (!q.Any())
                {
                    if (!read())
                    {
                        IsEof = true;
                        return "";
                    }
                }

                return q.Dequeue();
            }

            public static int NextInt() => int.Parse(Next());
            public static long NextLong() => long.Parse(Next());
            public static double NextDouble() => double.Parse(Next());

            public static List<string> Next(int n) => Enumerable.Range(0, n).Select(_ => Next()).ToList();
            public static List<int> NextInt(int n) => Next(n).Select(x => int.Parse(x)).ToList();
            public static List<long> NextLong(int n) => Next(n).Select(x => long.Parse(x)).ToList();
            public static List<double> NextDouble(int n) => Next(n).Select(x => double.Parse(x)).ToList();

            public static List<string> NextLine() => Console.ReadLine().Trim().Split(separator, StringSplitOptions.RemoveEmptyEntries).ToList();
            public static List<int> NextIntLine() => NextLine().Select(x => int.Parse(x)).ToList();
            public static List<long> NextLongLine() => NextLine().Select(x => long.Parse(x)).ToList();
            public static List<double> NextDoubleLine() => NextLine().Select(x => double.Parse(x)).ToList();
        }
        private static bool isPrime(long x)
        {
            if (x == 2) { return true; }
            if (x < 2 || x % 2 == 0) { return false; }
            long i = 3;
            while (i * i <= x)
            {
                if (x % i == 0) { return false; }
                i = i + 2;
            }
            return true;
        }
        private static long lcm(long x, long y)
        {
            return x / gcd(x, y) * y;
        }
        private static long gcd(long x, long y)
        {
            return y > 0 ? gcd(y, x % y) : x;
        }
        private static long pow(long x, long n)
        {
            if (n == 0) { return 1; }
            long res = pow(x * x % MOD, n / 2);
            if (n % 2 == 1)
            {
                res = res * x % MOD;
            }
            return res;
        }
        private static void Swap<T>(ref T x, ref T y)
        {
            T t = x;
            x = y;
            y = t;
        }

        /// <summary>
        /// 指定した値以上の先頭のインデクスを返す
        /// </summary>
        /// <typeparam name="T">比較する値の型</typeparam>
        /// <param name="arr">対象の配列（※ソート済みであること）</param>
        /// <param name="start">開始インデクス [inclusive]</param>
        /// <param name="end">終了インデクス [exclusive]</param>
        /// <param name="value">検索する値</param>
        /// <param name="comparer">比較関数(インターフェイス)</param>
        /// <returns>指定した値以上の先頭のインデクス</returns>
        public static int LowerBound<T>(IReadOnlyList<T> arr, int start, int end, T value, IComparer<T> comparer)
        {
            int low = start;
            int high = end;
            int mid;
            while (low < high)
            {
                mid = ((high - low) >> 1) + low;
                if (comparer.Compare(arr[mid], value) < 0)
                    low = mid + 1;
                else
                    high = mid;
            }
            return low;
        }

        //引数省略のオーバーロード
        public static int LowerBound<T>(IReadOnlyList<T> arr, T value) where T : IComparable
        {
            return LowerBound(arr, 0, arr.Count, value, Comparer<T>.Default);
        }

        /// <summary>
        /// 指定した値より大きい先頭のインデクスを返す
        /// </summary>
        /// <typeparam name="T">比較する値の型</typeparam>
        /// <param name="arr">対象の配列（※ソート済みであること）</param>
        /// <param name="start">開始インデクス [inclusive]</param>
        /// <param name="end">終了インデクス [exclusive]</param>
        /// <param name="value">検索する値</param>
        /// <param name="comparer">比較関数(インターフェイス)</param>
        /// <returns>指定した値より大きい先頭のインデクス</returns>
        public static int UpperBound<T>(IReadOnlyList<T> arr, int start, int end, T value, IComparer<T> comparer)
        {
            int low = start;
            int high = end;
            int mid;
            while (low < high)
            {
                mid = ((high - low) >> 1) + low;
                if (comparer.Compare(arr[mid], value) <= 0)
                    low = mid + 1;
                else
                    high = mid;
            }
            return low;
        }

        //引数省略のオーバーロード
        public static int UpperBound<T>(IReadOnlyList<T> arr, T value)
        {
            return UpperBound(arr, 0, arr.Count, value, Comparer<T>.Default);
        }
        #endregion
    }

    public class DisjointSet
    {
        private int[] rank;
        private int[] p;
        private int[] size;
        public DisjointSet(int n)
        {
            rank = new int[n];
            p = new int[n];
            size = new int[n];
            for (int i = 0; i < n; ++i)
            {
                MakeSet(i);
            }
        }
        public void MakeSet(int x)
        {
            p[x] = x;
            rank[x] = 0;
            size[x] = 1;
        }
        public bool IsSame(int x, int y)
        {
            return FindSet(x) == FindSet(y);
        }
        public void Unite(int x, int y)
        {
            Link(FindSet(x), FindSet(y));
        }
        public void Link(int x, int y)
        {
            if (rank[x] > rank[y])
            {
                p[y] = x;
                size[x] += size[y];
                size[y] = 0;
            }
            else
            {
                p[x] = y;
                size[y] += size[x];
                size[x] = 0;
                if (rank[x] == rank[y])
                {
                    rank[y]++;
                }
            }
        }
        public int FindSet(int x)
        {
            if (x != p[x])
            {
                p[x] = FindSet(p[x]);
            }
            return p[x];
        }
        public int Size(int x)
        {
            int root = FindSet(x);
            return size[root];
        }
    }
    public class PriorityQueue<T> where T : IComparable
    {
        private IComparer<T> _comparer = null;
        private int _type = 0;

        private T[] _heap;
        private int _sz = 0;

        private int _count = 0;

        /// <summary>
        /// Priority Queue with custom comparer
        /// </summary>
        public PriorityQueue(int maxSize, IComparer<T> comparer)
        {
            _heap = new T[maxSize];
            _comparer = comparer;
        }

        /// <summary>
        /// Priority queue
        /// </summary>
        /// <param name="maxSize">max size</param>
        /// <param name="type">0: asc, 1:desc</param>
        public PriorityQueue(int maxSize, int type = 0)
        {
            _heap = new T[maxSize];
            _type = type;
        }

        private int Compare(T x, T y)
        {
            if (_comparer != null) return _comparer.Compare(x, y);
            return _type == 0 ? x.CompareTo(y) : y.CompareTo(x);
        }

        public void Push(T x)
        {
            _count++;

            //node number
            var i = _sz++;

            while (i > 0)
            {
                //parent node number
                var p = (i - 1) / 2;

                if (Compare(_heap[p], x) <= 0) break;

                _heap[i] = _heap[p];
                i = p;
            }

            _heap[i] = x;
        }

        public T Pop()
        {
            _count--;

            T ret = _heap[0];
            T x = _heap[--_sz];

            int i = 0;
            while (i * 2 + 1 < _sz)
            {
                //children
                int a = i * 2 + 1;
                int b = i * 2 + 2;

                if (b < _sz && Compare(_heap[b], _heap[a]) < 0) a = b;

                if (Compare(_heap[a], x) >= 0) break;

                _heap[i] = _heap[a];
                i = a;
            }

            _heap[i] = x;

            return ret;
        }

        public int Count()
        {
            return _count;
        }

        public T Peek()
        {
            return _heap[0];
        }

        public bool Contains(T x)
        {
            for (int i = 0; i < _sz; i++) if (x.Equals(_heap[i])) return true;
            return false;
        }

        public void Clear()
        {
            while (this.Count() > 0) this.Pop();
        }

        public IEnumerator<T> GetEnumerator()
        {
            var ret = new List<T>();

            while (this.Count() > 0)
            {
                ret.Add(this.Pop());
            }

            foreach (var r in ret)
            {
                this.Push(r);
                yield return r;
            }
        }

        public T[] ToArray()
        {
            T[] array = new T[_sz];
            int i = 0;

            foreach (var r in this)
            {
                array[i++] = r;
            }

            return array;
        }
    }
}