use std::collections::VecDeque;
use std::convert::TryInto;

struct Solution {}
impl Solution {
    pub fn shortest_path_binary_matrix(grid: Vec<Vec<i32>>) -> i32 {
        let n = grid.len();

        // create an array of distances
        let mut distances = grid.clone();
        for y in 0..n {
            for x in 0..n {
                distances[y][x] = -1;
            }
        }

        // initialize the start with an initial distance
        let mut q: VecDeque<(usize, usize)> = VecDeque::new();
        if grid[0][0] == 0 {
            distances[0][0] = 1;
            q.push_back((0, 0));
        }

        while let Some((y, x)) = q.pop_front() {
            if (y, x) == (n - 1, n - 1) {
                break;
            }

            for (next_y, next_x) in (-1_isize..=1)
                .flat_map(|dy| (-1_isize..=1).map(move |dx| (dy, dx)))
                .map(|(dy, dx)| (y as isize + dy, x as isize + dx))
                .filter(|&(next_y, next_x)| {
                    (next_y, next_x) != (y as isize, x as isize)
                        && next_y >= 0
                        && next_y < n.try_into().unwrap()
                        && next_x >= 0
                        && next_x < n.try_into().unwrap()
                })
            {
                let (next_y, next_x) = (next_y as usize, next_x as usize);

                if distances[next_y][next_x] == -1 && grid[next_y][next_x] == 0 {
                    distances[next_y][next_x] = distances[y][x] + 1;
                    q.push_back((
                        (next_y as isize).try_into().unwrap(),
                        (next_x as isize).try_into().unwrap(),
                    ));
                }
            }
        }

        distances[n - 1][n - 1]
    }
}

fn main() {
    assert_eq!(
        Solution::shortest_path_binary_matrix(vec![vec![0, 1], vec![1, 0]]),
        2
    );
    assert_eq!(
        Solution::shortest_path_binary_matrix(vec![vec![0, 0, 0], vec![1, 1, 0], vec![1, 1, 0]]),
        4
    );
    assert_eq!(
        Solution::shortest_path_binary_matrix(vec![vec![1, 0, 0], vec![1, 1, 0], vec![1, 1, 0]]),
        -1
    );
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn example_1() {
        assert_eq!(
            Solution::shortest_path_binary_matrix(vec![vec![0, 1], vec![1, 0]]),
            2
        );
    }

    #[test]
    fn example_2() {
        assert_eq!(
            Solution::shortest_path_binary_matrix(vec![
                vec![0, 0, 0],
                vec![1, 1, 0],
                vec![1, 1, 0]
            ]),
            4
        );
    }

    #[test]
    fn example_3() {
        assert_eq!(
            Solution::shortest_path_binary_matrix(vec![
                vec![1, 0, 0],
                vec![1, 1, 0],
                vec![1, 1, 0]
            ]),
            -1
        );
    }
}