Function count_pairs_at_distance 

pub fn count_pairs_at_distance(graph: &Graph, k: u32) -> IgraphResult<u64>

Compute the number of vertex pairs at a given distance.

More general version: counts pairs at distance exactly k. For undirected graphs, counts unordered pairs; for directed, counts ordered pairs.

Examples

use rust_igraph::{Graph, count_pairs_at_distance};

let g = Graph::from_edges(&[(0,1),(1,2),(2,3),(3,4)], false, Some(5)).unwrap();
// Distance 2: {0,2}, {1,3}, {2,4} = 3 pairs
assert_eq!(count_pairs_at_distance(&g, 2).unwrap(), 3);