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 Rust (1.42.0) (judge verdict: Accepted)

#![allow(unused_imports)]
use std::collections::{HashMap, HashSet, VecDeque};
use std::iter::FromIterator;
// use itertools::Itertools;
use proconio::{input, marker::*};

type Point = (usize, usize);

fn main() {
    input! {
        h: usize,
        w: usize,
        ch: Usize1,
        cw: Usize1,
        dh: Usize1,
        dw: Usize1,
        sss: [Chars; h],
    };

    let (spaces, point_to_space_index) = make_spaces(h, w, &sss);

    if spaces.len() == 1 {
        println!("0");
        return;
    }
    let c_index = *point_to_space_index.get(&(cw, ch)).unwrap();
    let d_index = *point_to_space_index.get(&(dw, dh)).unwrap();

    println!(
        "{}",
        search_count(h, w, spaces, c_index, d_index, point_to_space_index)
    );
}

fn make_spaces(
    h: usize,
    w: usize,
    sss: &Vec<Vec<char>>,
) -> (Vec<Vec<Point>>, HashMap<Point, usize>) {
    let mut spaces: Vec<Vec<Point>> = vec![];
    // space = vec![(0, 0), (0, 1), (0, 2), (1, 2)];
    let mut point_to_space_index: HashMap<Point, usize> = HashMap::new();
    let mut viewed_points: HashSet<Point> = HashSet::new();
    let mut index = 0usize;

    for y in 0usize..h {
        for x in 0usize..w {
            let point: Point = (x, y);
            if viewed_points.contains(&point) {
                continue;
            } else {
                viewed_points.insert(point);
            }
            if sss[y][x] == '.' {
                // 新規のスペースを発見
                let mut space: Vec<Point> = vec![point];
                let space_index = index;
                point_to_space_index.insert(point, space_index);
                let mut queue: VecDeque<Point> = VecDeque::new();
                queue.push_back(point);
                while let Some((qpx, qpy)) = queue.pop_front() {
                    let check_points: Vec<Point> = {
                        let mut tmp: Vec<Point> = vec![];
                        if qpx > 0 {
                            tmp.push((qpx - 1, qpy));
                        }
                        if qpx < w - 1 {
                            tmp.push((qpx + 1, qpy));
                        }
                        if qpy > 0 {
                            tmp.push((qpx, qpy - 1));
                        }
                        if qpy < h - 1 {
                            tmp.push((qpx, qpy + 1));
                        }
                        tmp
                    };
                    for check_point in check_points {
                        if viewed_points.contains(&check_point) {
                            continue;
                        } else {
                            viewed_points.insert(check_point);
                            let (cx, cy) = check_point;
                            if sss[cy][cx] == '.' {
                                point_to_space_index.insert(check_point, space_index);
                                space.push(check_point);
                                queue.push_back(check_point);
                            }
                        }
                    }
                }
                spaces.push(space);
                index += 1;
            }
        }
    }
    return (spaces, point_to_space_index);
}

fn search_count(
    h: usize,
    w: usize,
    spaces: Vec<Vec<Point>>,
    c_index: usize,
    d_index: usize,
    point_to_space_index: HashMap<Point, usize>,
) -> isize {
    let warpable_areas: Vec<HashSet<Point>> = spaces
        .iter()
        .map(|space| {
            let mut warpable_area = HashSet::new();
            let inner: HashSet<&Point> = HashSet::from_iter(space.iter());
            for &(x, y) in space {
                let up_y = std::cmp::max(y as isize - 2, 0) as usize;
                let down_y = std::cmp::min(y as isize + 2, h as isize - 1) as usize;
                for y in up_y..=down_y {
                    let left_x = std::cmp::max(x as isize - 2, 0) as usize;
                    let right_x = std::cmp::min(x as isize + 2, w as isize - 1) as usize;
                    for x in left_x..=right_x {
                        let p = (x, y);
                        if !inner.contains(&p) {
                            warpable_area.insert(p);
                        }
                    }
                }
            }
            return warpable_area;
        })
        .collect();

    let mut viewed_index = HashSet::new();
    viewed_index.insert(c_index);
    let mut queue: VecDeque<Vec<usize>> = VecDeque::new();
    queue.push_back(vec![c_index]);
    let mut count = 1;
    while let Some(indexes) = queue.pop_front() {
        let mut next_indexes = vec![];
        for index in indexes {
            let warpable_area = &warpable_areas[index];
            for &point in warpable_area {
                if let Some(&warpable_index) = point_to_space_index.get(&point) {
                    if warpable_index == d_index {
                        return count;
                    }
                    if !viewed_index.contains(&warpable_index) {
                        viewed_index.insert(warpable_index);
                        next_indexes.push(warpable_index);
                    }
                }
            }
        }
        count += 1;
        if !next_indexes.is_empty() {
            queue.push_back(next_indexes);
        }
    }
    return -1;
}