Use an indexed vec for visited.

Author: Totodore

src/bfs.rs

@@ -26,20 +26,22 @@ impl Graph {
 /// Naive BFS implementation using Vec as a queue (intentionally slow)
 /// Returns the order in which nodes were visited
 pub fn bfs_naive(graph: &Graph, start: usize) -> Vec<usize> {
-    let mut visited = HashSet::new();
+    let mut visited = Vec::from_iter((0..graph.num_nodes()).map(|_| false));
     let mut queue = VecDeque::with_capacity(1024);
     let mut result = Vec::with_capacity(graph.num_nodes());
 
     queue.push_back(start);
-    visited.insert(start);
+    visited[start] = true;
 
     while !queue.is_empty() {
         let node = queue.pop_front().unwrap();
         result.push(node);
 
         if let Some(neighbors) = graph.adjacency.get(node) {
             for &neighbor in neighbors {
-                if visited.insert(neighbor) {
+                let prev = visited[neighbor];
+                visited[neighbor] = true;
+                if prev {
                     queue.push_back(neighbor);
                 }
             }