Function graphalgs::shortest_path::spfa

pub fn spfa<G>(
    graph: G,
    source: G::NodeId
) -> Result<(Vec<G::EdgeWeight>, Vec<Option<G::NodeId>>), NegativeCycle>where
    G: IntoEdges + IntoNodeIdentifiers + NodeIndexable,
    G::EdgeWeight: FloatMeasure,

Shortest Path Faster Algorithm. Compute shortest distances from node source to all other.

Compute shortest paths lengths in a weighted graph with positive or negative edge weights, but with no negative cycles.

Arguments

• graph: weighted graph.
• source: the source vertex, for which we calculate the lengths of the shortest paths to all the others.

Returns

• Err: if graph contains negative cycle.
• Ok: a pair of a vector of shortest distances and a vector of predecessors of each vertex along the shortest path.

Examples

use petgraph::Graph;
use graphalgs::shortest_path::spfa;

let mut g = Graph::new();
let a = g.add_node(()); // node with no weight
let b = g.add_node(());
let c = g.add_node(());
let d = g.add_node(());
let e = g.add_node(());
let f = g.add_node(());
g.extend_with_edges(&[
    (0, 1, 3.0),
    (0, 3, 2.0),
    (1, 2, 1.0),
    (1, 5, 7.0),
    (2, 4, -4.0),
    (3, 4, -1.0),
    (4, 5, 1.0),
]);

// Graph represented with the weight of each edge.
//
//     3       1
// a ----- b ----- c
// | 2     | 7     |
// d       f       | -4
// | -1    | 1     |
// \------ e ------/

assert_eq!(spfa(&g, a), Ok((vec![0.0 ,     3.0,     4.0,    2.0,     0.0,     1.0],
                            vec![None, Some(a), Some(b), Some(a), Some(c), Some(e)]
                          ))
          );


// Negative cycle.
let graph = Graph::<(), f32>::from_edges(&[
    (0, 1, 2.0), (1, 2, 2.0), (2, 0, -10.0)]);

assert!(spfa(&graph, 0.into()).is_err());