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 Java (OpenJDK 11.0.6) (judge verdict: Time Limit Exceeded)


import java.io.IOException;
import java.io.InputStream;
import java.math.BigInteger;
import java.util.*;
import java.util.List;
import java.util.jar.JarEntry;
import java.util.stream.Collectors;
import java.util.stream.IntStream;
import java.util.stream.LongStream;

import static java.lang.Math.max;
import static java.lang.Math.min;
import static java.lang.Math.pow;

import static java.lang.String.format;


public class Main {
    private static final String PAIRWISE = "pairwise coprime";
    private static final String SETWISE = "setwise coprime";
    private static final String NOT = "not coprime";
    static final int[] dx = {-1, 1, 0, 0};
    static final int[] dy = {0, 0, -1, 1};
    private static final int INF = Integer.MAX_VALUE >> 4;
    public static void main(String[] args) {
        Scanner scanner=new Scanner();
        int h = scanner.nextInt();
        int w = scanner.nextInt();
        int ch = scanner.nextInt()-1;
        int cw = scanner.nextInt()-1;
        int dh = scanner.nextInt()-1;
        int dw = scanner.nextInt()-1;
        boolean[][] isWall = new boolean[h][w];
        for (int i = 0; i < h; i++) {
            String s = scanner.next();
            for (int j = 0; j < w; j++) {
                isWall[i][j] = s.charAt(j) == '#';
            }
        }
        int[][] ans = new int[h][w];
        for (int i = 0; i < h; i++) {
            Arrays.fill(ans[i], INF);
        }
//        put(Arrays.deepToString(ans));
        ans[ch][cw] = 0;
        Deque<FixedPair> deq = new ArrayDeque<>();
        deq.add(new FixedPair(ch, cw));
        int cnt=0;
        while (!deq.isEmpty()) {
//            put(deq);
            Set<FixedPair> set = new HashSet<>();
            while (!deq.isEmpty()) {
                var fp = deq.removeFirst();
                ans[fp.x][fp.y] = cnt;
                set.add(fp);
                for (int i = 0; i < 4; i++) {
                    FixedPair next = new FixedPair(fp.x + dx[i], fp.y + dy[i]);
                    if(next.x<0||next.x>=h||next.y<0||next.y>=w)continue;
                    if(isWall[next.x][next.y])continue;
                    if(ans[next.x][next.y]==cnt)continue;
                    deq.addLast(next);
                }
            }
//            put(Arrays.deepToString(ans));
//            put(set);
            cnt++;
            for (var fp : set) {
                for (int i = -2; i <= 2; i++) {
                    for (int j = -2; j <= 2; j++) {
                        if(i==0&&j==0)continue;
                        var next = new FixedPair(fp.x + i, fp.y + j);
                        if(next.x<0||next.x>=h||next.y<0||next.y>=w)continue;
                        if(isWall[next.x][next.y])continue;
                        if(ans[next.x][next.y]<=cnt)continue;
                        deq.addLast(next);
                        ans[next.x][next.y]=cnt;

                    }
                }
            }
//            put(deq);
        }
        put(ans[dh][dw] == INF ? -1 : ans[dh][dw]);


    }
    static class Container<T>{
        FixedPair point;
        T value;

        public Container(FixedPair p, T value) {
            this.point = p;
            this.value = value;
        }
        public FixedPair point(){return point;}
        public T value(){return value;}

        @Override
        public String toString() {
            return String.format("%s->%s",point,value);
        }
    }
    interface EnterExit extends Runnable{
        void enter();
        void exit();
        static Runnable build(EnterExit ee){
            return ()->{
                ee.enter();
                ee.run();
                ee.exit();
            };
        }
        default Runnable build(){return build(this);}
        static EnterExit measureTime(Runnable r){
            return new EnterExit() {
                private long enter;
                @Override
                public void enter() {
                    this.enter = System.currentTimeMillis();
                }

                @Override
                public void exit() {
                    put(System.currentTimeMillis()-enter+"[ms]");
                }

                @Override
                public void run() {
                    r.run();
                }
            };
        }
    }
    static class PrimeTable {
        private final int[] divisor;
        private final List<Integer> primes = new ArrayList<>();

        public PrimeTable(int n) {
            this.divisor = new int[n];
            for (int i = 2; i < n; i++) {
                if (divisor[i] != 0) continue;
                divisor[i] = i;
                primes.add(i);
                for (int j = i + i; j < n; j += i) {
                    if (divisor[j] == 0) divisor[j] = i;
                }
            }
        }

        public Map<Integer, Integer> primeFactorize(int x) {
            Map<Integer, Integer> res = new HashMap<>();
            while (divisor[x] != 0) {
                res.merge(divisor[x], 1, Integer::sum);
                x /= divisor[x];
            }
            return res;
        }

        @Override
        public String toString() {
            return Arrays.toString(divisor) + ":" + primes;
        }
    }

    public static int upper_bound(int[] a,int val){
        return upper_bound(a,0,a.length,val);
    }
    public static int upper_bound(int[] a,int l,int r,int val){
        if(r-l==1){
            if(a[l]>val) return l;
            return r;
        }
        int mid=(l+r)/2;
        if(a[mid]>val){
            return upper_bound(a,l,mid,val);
        }else{
            return upper_bound(a,mid,r,val);
        }
    }
    public static <T> int upper_bound(T[] a,int l,int r,T val,Comparator<T> comparator){
        if(r-l==1){
            if(comparator.compare(a[l],val)>0) return l;
            return r;
        }
        int mid=(l+r)/2;
        if(comparator.compare(a[mid],val)>0){
            return upper_bound(a,l,mid,val,comparator);
        }else{
            return upper_bound(a,mid,r,val,comparator);
        }
    }
    public static int lower_bound(int[] a,int val){
        return lower_bound(a,0,a.length,val);
    }
    public static int lower_bound(int[] a,int l,int r,int val){
        if(r-l==1){
            if(a[l]<val) return r;
            return l;
        }
        int mid=(l+r)/2;
        if(a[mid]<val){
            return lower_bound(a,mid,r,val);
        }else{
            return lower_bound(a,l,mid,val);
        }

    }

    public static <T> int lower_bound(T[] a,int l,int r,T val,Comparator<T> comparator){
        if(r-l==1){
            if(comparator.compare(a[l],val)<0) return r;
            return l;
        }
        int mid=(l+r)/2;
        if(comparator.compare(a[mid],val)<0){
            return lower_bound(a,mid,r,val,comparator);
        }else{
            return lower_bound(a,l,mid,val,comparator);
        }
    }


    public static void print(Object object){
        System.out.print(object);
    }
    public static void put(Object object) {
        System.out.println(object);
    }
    public static void put(){
        System.out.println();
    }

    final static private class Scanner {
        private final InputStream in = System.in;
        private final byte[] buffer = new byte[1024];
        private int ptr = 0;
        private int buflen = 0;

        private boolean hasNextByte() {
            if (ptr < buflen) {
                return true;
            } else {
                ptr = 0;
                try {
                    buflen = in.read(buffer);
                } catch (IOException e) {
                    e.printStackTrace();
                }
                if (buflen <= 0) {
                    return false;
                }
            }
            return true;
        }

        private int readByte() {
            if (hasNextByte())
                return buffer[ptr++];
            else
                return -1;
        }

        private boolean isPrintableChar(int c) {
            return 33 <= c && c <= 126;
        }

        public boolean hasNext() {
            while (hasNextByte() && !isPrintableChar(buffer[ptr]))
                ptr++;
            return hasNextByte();
        }

        public String next() {
            if (!hasNext())
                throw new NoSuchElementException();
            StringBuilder sb = new StringBuilder();
            int b = readByte();
            while (isPrintableChar(b)) {
                sb.appendCodePoint(b);
                b = readByte();
            }
            return sb.toString();
        }

        public long nextLong() {
            if (!hasNext())
                throw new NoSuchElementException();
            long n = 0;
            boolean minus = false;
            int b = readByte();
            if (b == '-') {
                minus = true;
                b = readByte();
            }
            if (b < '0' || '9' < b) {
                throw new NumberFormatException();
            }
            while (true) {
                if ('0' <= b && b <= '9') {
                    n *= 10;
                    n += b - '0';
                } else if (b == -1 || !isPrintableChar(b)) {
                    return minus ? -n : n;
                } else {
                    throw new NumberFormatException();
                }
                b = readByte();
            }
        }

        public int nextInt() {
            long nl = nextLong();
            if (nl < Integer.MIN_VALUE || nl > Integer.MAX_VALUE)
                throw new NumberFormatException();
            return (int) nl;
        }

        public double nextDouble() {
            return Double.parseDouble(next());
        }
    }
    final static private class FixedPair {
        final private int x, y;
        final static public FixedPair ZEROS=new FixedPair(0,0);
        FixedPair(int x, int y) {
            this.x = x;
            this.y = y;
        }

        public int getX() {
            return x;
        }

        public int getY() {
            return y;
        }

        @Override
        public int hashCode() {
            return (int)x+(int)y;
        }

        @Override
        public boolean equals(Object obj) {
            boolean result=super.equals(obj);
            if(obj.getClass()!=this.getClass()){
                return false;
            }
            FixedPair pair=(FixedPair)obj;
            if(this.x==pair.x&&this.y==pair.y) return true;
            return false;
        }

        @Override
        public String toString() {
            return String.format("(%d,%d)", x, y);
        }
    }
    final static private class Tuple<T,V>{
        //immutabl1でないことに注意(T,Vがmutableの場合変更可能)
        final private T t;
        final private V v;
        Tuple(T t,V v){
            this.t=t;
            this.v=v;
        }

        public T getT() {
            return t;
        }

        public V getV() {
            return v;
        }

        @Override
        public int hashCode() {
            return (t.hashCode()+v.hashCode());
        }

        @Override
        @SuppressWarnings("unchecked")
        public boolean equals(Object obj) {
            if(obj.getClass()!=this.getClass()){
                return false;
            }
            Tuple<T,V> tuple=(Tuple<T, V>) obj;
            return tuple.t.equals(this.t)&&tuple.v.equals(this.v);
        }

        @Override
        public String toString() {
            return String.format("<Tuple>=<%s,%s>",t,v);
        }
    }
    final static private class Util {
        static long gcd(long a,long b){
            //最大公約数　
            if(a%b==0)return b;
            return gcd(b,a%b);
        }

        static int gcd(int a, int b) {
            if(a%b==0)return b;
            return gcd(b, a % b);
        }
        static long lcm(long a,long b){
            //最小公倍数
            long gcd=gcd(a,b);
            long result=b/gcd;
            return a*result;
        }
        static long kaijoMod(int n,int mod){
            if(n<1) return -1;
            long result=1;
            for(int i=n;i>1;i--){
                result*=i;
                result%=mod;
            }
            return result;
        }
        static <T extends Comparable<T>> Map<T,Integer> count(List<T> list){
            //副作用
            Collections.sort(list);
            Map<T,Integer> result=new HashMap<>();
            int l=0,r=0;
            while(l<list.size()){
                while(r<list.size()-1&&list.get(r).equals(r+1)){
                    r++;
                }
                result.put(list.get(r),r-l+1);
                r++;
                l=r;
            }
            return result;

        }
        static Map<Integer,Integer> count(int[] array){
            //副作用
            Arrays.sort(array);
            Map<Integer,Integer> result=new HashMap<>();
            int l=0,r=0;
            while(l<array.length){
                while(r<array.length-1&&array[r]==array[r+1]){
                    r++;
                }
                result.put(array[l],r-l+1);
                r++;
                l=r;
            }
            return result;
        }
        static <T> String toStringBWS(Iterable<T> iterable){
            Iterator<T> ite=iterable.iterator();
            return toStringBWS(ite);
        }
        static <T> String toStringBWS(Iterator<T> ite){
            StringBuilder sb=new StringBuilder();
            sb.append(ite.next());
            while(ite.hasNext()){
                sb.append(" ");
                sb.append(ite.next());
            }
            return sb.toString();
        }
        static int[] factoringInPrimeNumbers(long n,int size){
            //素因数分解
            //sizeがnに比べて小さい場合完全に素因数分解出来ていない可能性がある
            int[] result=new int[size];
            for(int i=2;n>1&&i< result.length;i++){
                while(n%i==0){
                    result[i]++;
                    n/=i;
                }
            }
            return result;

        }
    }
}