breath first search algorithm

fn bfs(graph: &Graph, start: usize, end: usize) -> Option<usize> {
    let mut q = VecDeque::new();
    let mut visited = vec![false; graph.len()];
    q.push_back(start);
    visited[start] = true;
    while !q.is_empty() {
        let node = q.pop_front().unwrap();
        if node == end {
            return Some(node);
        }
        for &neighbour in &graph[node] {
            if !visited[neighbour] {
            visited[neighbour] = true;
            q.push_back(neighbour);
            }
        }
    }
    None
}