Function cycle

tests/test_undirected_graph.rs:130–135

()

#[test]
fn cycle() {
    let graph = create_graph(TINY_G);
    let c = Cycle::new(graph.as_ref());
    assert!(c.has_cycle());
    assert!(c.cycle().unwrap().eq(vec![3, 4, 5, 3].iter()));
}

#[test]
fn two_color() {