problems(rs): add „200. Number of Islands“

Signed-off-by: Matej Focko <mfocko@redhat.com>

problems/number-of-islands.rs

@@ -0,0 +1,92 @@
+use std::collections::{HashSet, VecDeque};
+
+type Position = (i32, i32);
+type Grid = Vec<Vec<char>>;
+
+impl Solution {
+    fn indices(grid: &Grid) -> impl Iterator<Item = Position> + '_ {
+        (0..grid.len() as i32)
+            .flat_map(move |y| (0..grid[y as usize].len() as i32).map(move |x| (y, x)))
+    }
+
+    fn interesting(grid: &Grid, visited: &HashSet<Position>, p: &Position) -> bool {
+        let (max_y, max_x) = (grid.len() as i32, grid[0].len() as i32);
+        let &(y, x) = p;
+
+        y >= 0
+            && y < max_y
+            && x >= 0
+            && x < max_x
+            && grid[p.0 as usize][p.1 as usize] != '0'
+            && !visited.contains(p)
+    }
+
+    fn bfs(grid: &Grid, visited: &mut HashSet<Position>, pos: Position) {
+        let mut queue: VecDeque<Position> = VecDeque::new();
+        queue.push_back(pos);
+        visited.insert(pos);
+
+        while let Some(p) = queue.pop_front() {
+            for d in [-1, 1] {
+                for adjacent in [(p.0 + d, p.1), (p.0, p.1 + d)] {
+                    if Solution::interesting(grid, visited, &adjacent) {
+                        queue.push_back(adjacent);
+                        visited.insert(adjacent);
+                    }
+                }
+            }
+        }
+    }
+
+    pub fn num_islands(grid: Grid) -> i32 {
+        let mut visited: HashSet<Position> = HashSet::new();
+
+        let mut islands = 0;
+        for (y, x) in Solution::indices(&grid) {
+            if !Solution::interesting(&grid, &visited, &(y, x)) {
+                continue;
+            }
+
+            Solution::bfs(&grid, &mut visited, (y, x));
+            islands += 1;
+        }
+
+        islands
+    }
+}
+struct Solution {}
+
+fn main() {
+    println!("Hello World!");
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_example_1() {
+        assert_eq!(
+            Solution::num_islands(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
+        );
+    }
+
+    #[test]
+    fn test_example_2() {
+        assert_eq!(
+            Solution::num_islands(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
+        );
+    }
+}