Token_swapper fails on graphs with edgeless nodes #994
Description
Information
Recently (see #971) the token swapper algorithm has been extended to support disconnected coupling maps, and in particular return an error rather than internally panic when swapping is not possible.
Here is an example where token swapper still internally panics.
let mut g = petgraph::graph::UnGraph::<(), ()>::new_undirected();
let a = g.add_node(());
let b = g.add_node(());
let c = g.add_node(());
let d = g.add_node(());
g.add_edge(c, d, ());
let mapping = HashMap::from([(a, b), (b, a)]);
let out = token_swapper(&g, mapping, Some(10), Some(4), Some(50));
Ideally this should return Err(MapNotPossible) instead of panicking:
panicked at 'index out of bounds: the len is 0 but the index is 0', rustworkx-core\src\token_swapper.rs:305:40