Function petgraph::algo::connected_components

pub fn connected_components<G>(g: G) -> usize where
    G: NodeCompactIndexable + IntoEdgeReferences, 

[Generic] Return the number of connected components of the graph.

For a directed graph, this is the weakly connected components.

Example

use petgraph::Graph;
use petgraph::algo::connected_components;
use petgraph::prelude::*;

let mut graph : Graph<(),(),Directed>= Graph::new();
let a = graph.add_node(()); // node with no weight
let b = graph.add_node(());
let c = graph.add_node(());
let d = graph.add_node(());
let e = graph.add_node(());
let f = graph.add_node(());
let g = graph.add_node(());
let h = graph.add_node(());

graph.extend_with_edges(&[
    (a, b),
    (b, c),
    (c, d),
    (d, a),
    (e, f),
    (f, g),
    (g, h),
    (h, e)
]);
// a ----> b       e ----> f
// ^       |       ^       |
// |       v       |       v
// d <---- c       h <---- g

assert_eq!(connected_components(&graph),2);
graph.add_edge(b,e,());
assert_eq!(connected_components(&graph),1);