LeetCode/rs/2024-04-19-number-of-islands.rs

use std::collections::VecDeque;

impl Solution {
    fn dimensions(grid: &[Vec<char>]) -> (usize, usize) {
        (grid.len(), grid[0].len())
    }

    fn in_range(grid: &[Vec<char>], x: isize, y: isize) -> bool {
        y >= 0 && y < grid.len() as isize && x >= 0 && x < grid[y as usize].len() as isize
    }

    fn get_neighbors(
        grid: &[Vec<char>],
        visited: &[Vec<bool>],
        x: isize,
        y: isize,
    ) -> Vec<(isize, isize)> {
        [-1, 1]
            .into_iter()
            .flat_map(|d| [(x + d, y), (x, y + d)])
            .filter(|&(x, y)| {
                Self::in_range(grid, x, y)
                    && !visited[y as usize][x as usize]
                    && grid[y as usize][x as usize] == '1'
            })
            .collect()
    }

    fn bfs(grid: &[Vec<char>], visited: &mut [Vec<bool>], x: isize, y: isize) {
        let mut q: VecDeque<(isize, isize)> = VecDeque::from([(x, y)]);
        visited[y as usize][x as usize] = true;

        while let Some((x, y)) = q.pop_back() {
            Self::get_neighbors(grid, visited, x, y)
                .into_iter()
                .for_each(|(x, y)| {
                    q.push_back((x, y));
                    visited[y as usize][x as usize] = true;
                });
        }
    }

    pub fn num_islands(grid: Vec<Vec<char>>) -> i32 {
        let (m, n) = Self::dimensions(&grid);
        let mut visited = vec![vec![false; n]; m];

        let mut islands = 0;
        for idx in 0..m * n {
            let (y, x) = (idx / n, idx % n);

            if visited[y][x] || grid[y][x] == '0' {
                continue;
            }

            islands += 1;
            Self::bfs(&grid, &mut visited, x as isize, y as isize);
        }

        islands
    }
}