graphalgs 0.2.0

Graph algorithms based on the Rust 'petgraph' library.
Documentation 
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use petgraph::visit::{IntoEdges, IntoNeighbors, NodeIndexable, VisitMap, Visitable};
use std::collections::VecDeque;

/// The lengths of the shortest paths from the start vertex to all the others.
///
/// The algorithm is based on BFS, and the path length is equal to the number of edges in this path.
/// Returns ```Vec<f32>```, the i-th position of which stores the length of the path from the start node to the node with index i.
/// If it is impossible to get from the vertex x to the vertex y, then the distance from x to y will be equal to f32::INFINITY.
/// Time complexity: **O(|V| + |E|)**, where **|V|** is the number of vertices, and **|E|** is the number of edges in the graph.
///
/// # Examples
///
/// ```
/// use graphalgs::shortest_path::shortest_distances;
/// use petgraph::Graph;
///
/// let inf = f32::INFINITY;
/// let graph = Graph::<u8, ()>::from_edges(&[(0, 1), (0, 2), (1, 2)]);
///
/// assert_eq!(shortest_distances(&graph, 0.into()), vec![0.0, 1.0, 1.0]);
/// assert_eq!(shortest_distances(&graph, 1.into()), vec![inf, 0.0, 1.0]);
/// assert_eq!(shortest_distances(&graph, 2.into()), vec![inf, inf, 0.0]);
/// ```
pub fn shortest_distances<G>(graph: G, start: G::NodeId) -> Vec<f32>
where
    G: Visitable + NodeIndexable + IntoEdges + IntoNeighbors,
{
    let mut visit_map = graph.visit_map();
    visit_map.visit(start);

    let mut dist = vec![f32::INFINITY; graph.node_bound()];
    dist[graph.to_index(start)] = 0.0;

    let mut queue: VecDeque<G::NodeId> = VecDeque::new();
    queue.push_back(start);

    while !queue.is_empty() {
        let current = queue.pop_front().unwrap();
        for v in graph.neighbors(current) {
            if visit_map.visit(v) {
                queue.push_back(v);
                dist[graph.to_index(v)] = dist[graph.to_index(current)] + 1.0;
            }
        }
    }

    dist
}

#[cfg(test)]
mod tests {
    use super::*;
    use crate::generate::random_digraph;
    use crate::shortest_path::bellman_ford;
    use petgraph::graph::Graph;
    use petgraph::Directed;
    use rand::Rng;

    #[test]
    fn test_shortest_distances() {
        let inf = f32::INFINITY;

        let mut graph = Graph::<u8, ()>::new();
        let n0 = graph.add_node(0);
        let n1 = graph.add_node(1);
        let n2 = graph.add_node(2);
        let n3 = graph.add_node(3);
        let n4 = graph.add_node(4);
        let n5 = graph.add_node(5);
        let n6 = graph.add_node(6);
        let n7 = graph.add_node(7);
        let n8 = graph.add_node(8);
        let n9 = graph.add_node(9);
        let n10 = graph.add_node(10);
        let n11 = graph.add_node(11);

        graph.add_edge(n0, n1, ());
        graph.add_edge(n0, n2, ());
        graph.add_edge(n2, n3, ());
        graph.add_edge(n2, n5, ());
        graph.add_edge(n3, n4, ());
        graph.add_edge(n4, n8, ());
        graph.add_edge(n5, n9, ());
        graph.add_edge(n5, n6, ());
        graph.add_edge(n6, n3, ());
        graph.add_edge(n6, n7, ());
        graph.add_edge(n6, n10, ());
        graph.add_edge(n7, n8, ());
        graph.add_edge(n7, n11, ());
        graph.add_edge(n8, n11, ());
        graph.add_edge(n9, n1, ());
        graph.add_edge(n9, n10, ());
        graph.add_edge(n10, n6, ());
        graph.add_edge(n11, n6, ());
        graph.add_edge(n11, n10, ());
        graph.add_edge(n0, n9, ());

        assert_eq!(
            shortest_distances(&graph, graph.from_index(0)),
            vec![0.0, 1.0, 1.0, 2.0, 3.0, 2.0, 3.0, 4.0, 4.0, 1.0, 2.0, 5.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(1)),
            vec![inf, 0.0, inf, inf, inf, inf, inf, inf, inf, inf, inf, inf]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(2)),
            vec![inf, 3.0, 0.0, 1.0, 2.0, 1.0, 2.0, 3.0, 3.0, 2.0, 3.0, 4.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(3)),
            vec![inf, inf, inf, 0.0, 1.0, inf, 4.0, 5.0, 2.0, inf, 4.0, 3.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(4)),
            vec![inf, inf, inf, 4.0, 0.0, inf, 3.0, 4.0, 1.0, inf, 3.0, 2.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(5)),
            vec![inf, 2.0, inf, 2.0, 3.0, 0.0, 1.0, 2.0, 3.0, 1.0, 2.0, 3.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(6)),
            vec![inf, inf, inf, 1.0, 2.0, inf, 0.0, 1.0, 2.0, inf, 1.0, 2.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(7)),
            vec![inf, inf, inf, 3.0, 4.0, inf, 2.0, 0.0, 1.0, inf, 2.0, 1.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(8)),
            vec![inf, inf, inf, 3.0, 4.0, inf, 2.0, 3.0, 0.0, inf, 2.0, 1.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(9)),
            vec![inf, 1.0, inf, 3.0, 4.0, inf, 2.0, 3.0, 4.0, 0.0, 1.0, 4.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(10)),
            vec![inf, inf, inf, 2.0, 3.0, inf, 1.0, 2.0, 3.0, inf, 0.0, 3.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(11)),
            vec![inf, inf, inf, 2.0, 3.0, inf, 1.0, 2.0, 3.0, inf, 1.0, 0.0]
        );

        let mut graph = Graph::<u8, ()>::new();
        let n0 = graph.add_node(0);
        let n1 = graph.add_node(1);
        let n2 = graph.add_node(2);
        let n3 = graph.add_node(3);
        let n4 = graph.add_node(4);
        let n5 = graph.add_node(5);
        let n6 = graph.add_node(6);

        graph.add_edge(n0, n6, ());
        graph.add_edge(n0, n1, ());
        graph.add_edge(n1, n0, ());
        graph.add_edge(n1, n2, ());
        graph.add_edge(n1, n5, ());
        graph.add_edge(n1, n6, ());
        graph.add_edge(n2, n1, ());
        graph.add_edge(n2, n3, ());
        graph.add_edge(n3, n2, ());
        graph.add_edge(n3, n4, ());
        graph.add_edge(n4, n3, ());
        graph.add_edge(n4, n5, ());
        graph.add_edge(n5, n2, ());
        graph.add_edge(n5, n6, ());
        graph.add_edge(n5, n1, ());
        graph.add_edge(n5, n4, ());
        graph.add_edge(n6, n0, ());
        graph.add_edge(n6, n1, ());
        graph.add_edge(n6, n5, ());
        graph.add_edge(n2, n5, ());

        assert_eq!(
            shortest_distances(&graph, graph.from_index(0)),
            vec![0.0, 1.0, 2.0, 3.0, 3.0, 2.0, 1.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(1)),
            vec![1.0, 0.0, 1.0, 2.0, 2.0, 1.0, 1.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(2)),
            vec![2.0, 1.0, 0.0, 1.0, 2.0, 1.0, 2.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(3)),
            vec![3.0, 2.0, 1.0, 0.0, 1.0, 2.0, 3.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(4)),
            vec![3.0, 2.0, 2.0, 1.0, 0.0, 1.0, 2.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(5)),
            vec![2.0, 1.0, 1.0, 2.0, 1.0, 0.0, 1.0]
        );
        assert_eq!(
            shortest_distances(&graph, graph.from_index(6)),
            vec![1.0, 1.0, 2.0, 3.0, 2.0, 1.0, 0.0]
        );

        // Random tests

        let mut rng = rand::thread_rng();

        for n in 2..=50 {
            let graph = Graph::<(), f32, Directed, usize>::from_edges(
                random_digraph(n, rng.gen_range(1..n * (n - 1)))
                    .unwrap()
                    .into_iter()
                    .map(|edge| (edge.0, edge.1, 1.0)),
            );

            for v in 0..graph.node_count() {
                let sd_res = shortest_distances(&graph, v.into());
                let bf_res = bellman_ford(&graph, v.into()).unwrap().distances;
                assert_eq!(sd_res, bf_res);
            }
        }
    }
}