feat: add number of islands in rs

Author: bujosa

src/medium/number_of_islands.rs

@@ -0,0 +1,68 @@
+#![allow(dead_code)]
+pub fn num_islands(grid: &mut Vec<Vec<char>>) -> i32 {
+    if grid.is_empty() {
+        return 0;
+    }
+
+    let rows = grid.len();
+    let cols = grid[0].len();
+    let mut islands = 0;
+
+    fn dfs(grid: &mut Vec<Vec<char>>, i: usize, j: usize) {
+        let rows = grid.len();
+        let cols = grid[0].len();
+
+        if i >= rows || j >= cols || grid[i][j] == '0' {
+            return;
+        }
+
+        grid[i][j] = '0';
+
+        if i > 0 {
+            dfs(grid, i - 1, j);
+        }
+        if j > 0 {
+            dfs(grid, i, j - 1);
+        }
+        dfs(grid, i + 1, j);
+        dfs(grid, i, j + 1);
+    }
+
+    for i in 0..rows {
+        for j in 0..cols {
+            if grid[i][j] == '1' {
+                islands += 1;
+                dfs(grid, i, j);
+            }
+        }
+    }
+
+    islands
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_num_islands() {
+        assert_eq!(
+            num_islands(&mut vec![
+                vec!['1', '1', '1', '1', '0'],
+                vec!['1', '1', '0', '1', '0'],
+                vec!['1', '1', '0', '0', '0'],
+                vec!['0', '0', '0', '0', '0']
+            ]),
+            1
+        );
+        assert_eq!(
+            num_islands(&mut vec![
+                vec!['1', '1', '0', '0', '0'],
+                vec!['1', '1', '0', '0', '0'],
+                vec!['0', '0', '1', '0', '0'],
+                vec!['0', '0', '0', '1', '1']
+            ]),
+            3
+        );
+    }
+}