rs: add «200. Number of Islands»

Signed-off-by: Matej Focko <me@mfocko.xyz>

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

@@ -0,0 +1,61 @@
+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
+    }
+}