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 itertools::Itertools;
#[allow(unused_imports)]
use num::*;
use proconio::input;
#[allow(unused_imports)]
use proconio::marker::*;
#[allow(unused_imports)]
use std::collections::*;

#[derive(Clone)]
pub struct Graph {
    graph: WeightedGraph,
}
#[derive(Clone)]
pub struct WeightedGraph {
    graph: Vec<Vec<(usize, i64)>>,
    vn: usize,
}
pub type WeightedEdge = (usize, usize, i64);
impl WeightedGraph {
    pub fn new(edges: &[WeightedEdge], vn: usize) -> Self {
        let mut graph = vec![Vec::new(); vn];
        for &(u, v, w) in edges {
            graph[u].push((v, w));
            graph[v].push((u, w));
        }
        Self { graph, vn }
    }
    pub fn new_directed(edges: &[WeightedEdge], vn: usize) -> Self {
        let mut graph = vec![Vec::new(); vn];
        for &(u, v, w) in edges {
            graph[u].push((v, w));
        }
        Self { graph, vn }
    }
    pub fn add_directed_edge(&mut self, e: WeightedEdge) {
        self.graph[e.0].push((e.1, e.2));
    }
    pub fn add_edge(&mut self, e: WeightedEdge) {
        self.graph[e.0].push((e.1, e.2));
        self.graph[e.1].push((e.0, e.2));
    }
    pub fn shortest_path(&self, start: usize) -> Vec<Option<i64>> {
        let mut cost_list = vec![None; self.vn];
        let mut que = std::collections::VecDeque::new();
        cost_list[start] = Some(0);
        que.push_back(start);
        while let Some(u) = que.pop_front() {
            for &(v, w) in &self.graph[u] {
                if cost_list[v].is_some() && cost_list[v].unwrap() <= cost_list[u].unwrap() + w {
                    continue;
                }
                let new_cost = cost_list[u].unwrap() + w;
                cost_list[v] = Some(new_cost);
                if w == 0 {
                    que.push_front(v);
                } else {
                    que.push_back(v);
                }
            }
        }
        cost_list
    }
}
pub struct Grid {
    grid: Vec<Vec<char>>,
    h: usize,
    w: usize,
    ng_char: char,
}
pub type VertexTable = std::collections::HashMap<(usize, usize), usize>;
impl Grid {
    #[allow(dead_code)]
    const UDLR_DIRS: [(isize, isize); 4] = [(-1, 0), (1, 0), (0, -1), (0, 1)];
    pub fn new(grid: &[Vec<char>], ng_char: char) -> Self {
        assert!(grid.len() > 0);
        let grid = grid.into_iter().cloned().collect::<Vec<_>>();
        let h = grid.len();
        let w = grid[0].len();
        Self {
            grid,
            h,
            w,
            ng_char,
        }
    }
    pub fn to_graph(&self) -> (WeightedGraph, VertexTable) {
        let mut edges = Vec::new();
        let mut vertex_table = std::collections::HashMap::new();
        let mut v = 0;
        for i in 0..self.h {
            for j in 0..self.w {
                if self.grid[i][j] == self.ng_char {
                    continue;
                }
                let from = self.gen_vertex_if_needed((i, j), &mut vertex_table, &mut v);
                for di in -2..=2 {
                    for dj in -2..=2 {
                        if di == 0 && dj == 0 {
                            continue;
                        }
                        let new_i = i as isize + di;
                        let new_j = j as isize + dj;
                        if new_i < 0
                            || new_i >= self.h as isize
                            || new_j < 0
                            || new_j >= self.w as isize
                        {
                            continue;
                        }
                        let is_lrud = (new_i - i as isize).abs() + (new_j - j as isize).abs() == 1;
                        let new_i = new_i as usize;
                        let new_j = new_j as usize;
                        if self.grid[new_i][new_j] == self.ng_char {
                            continue;
                        }
                        let to =
                            self.gen_vertex_if_needed((new_i, new_j), &mut vertex_table, &mut v);
                        let cost = if is_lrud { 0 } else { 1 };
                        edges.push((from, to, cost));
                    }
                }
            }
        }
        let graph = WeightedGraph::new_directed(&edges, vertex_table.len());
        (graph, vertex_table)
    }
    fn gen_vertex_if_needed(
        &self,
        pos: (usize, usize),
        vertex_table: &mut VertexTable,
        cur_v: &mut usize,
    ) -> usize {
        if let Some(&v) = vertex_table.get(&pos) {
            return v;
        } else {
            let v = *cur_v;
            vertex_table.insert(pos, *cur_v);
            *cur_v += 1;
            return v;
        };
    }
}

fn solve() {
    input! {
        h: usize, _: usize,
        ch: Usize1, cw: Usize1,
        dh: Usize1, dw: Usize1,
        grid: [Chars; h]
    };

    let (graph, table) = Grid::new(&grid, '#').to_graph();
    let start = *table.get(&(ch, cw)).unwrap();
    let goal = *table.get(&(dh, dw)).unwrap();
    let res = graph.shortest_path(start)[goal].unwrap_or(-1);
    println!("{}", res);
}

fn main() {
    std::thread::Builder::new()
        .name("big stack size".into())
        .stack_size(256 * 1024 * 1024)
        .spawn(|| {
            solve();
        })
        .unwrap()
        .join()
        .unwrap();
}