Function map_model::connectivity::find_scc

pub fn find_scc(
    map: &Map, 
    constraints: PathConstraints
) -> (HashSet<LaneID>, HashSet<LaneID>)

Calculate the srongy connected components (SCC) of the part of the map accessible by constraints (ie, the graph of sidewalks or driving+bike lanes). The largest component is the "main" graph; the rest is disconnected. Returns (lanes in the largest "main" component, all other disconnected lanes)