problems(rs): add “1557. Minimum Number of Vertices to Reach All Nodes”

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

problems/minimum-number-of-vertices-to-reach-all-nodes.rs

@@ -0,0 +1,19 @@
+impl Solution {
+    pub fn find_smallest_set_of_vertices(n: i32, edges: Vec<Vec<i32>>) -> Vec<i32> {
+        // It should be possible to use topological ordering + BFS, but…
+
+        let mut is_reachable: Vec<bool> = vec![false; n as usize];
+        for dst in edges.iter().map(|edge| edge[1] as usize) {
+            is_reachable[dst] = true;
+        }
+
+        let mut result: Vec<i32> = vec![];
+        for (i, &reachable) in is_reachable.iter().enumerate() {
+            if !reachable {
+                result.push(i as i32);
+            }
+        }
+
+        result
+    }
+}