Function third_leap_zagreb 

pub fn third_leap_zagreb(graph: &Graph) -> IgraphResult<u64>

Compute the third leap Zagreb index.

LM₃(G) = Σ_v d(v)·d₂(v) where d(v) is the ordinary degree and d₂(v) is the second degree (count of vertices at distance 2).

Examples

use rust_igraph::{Graph, third_leap_zagreb};

// Path 0-1-2: d=[1,2,1], d₂=[1,0,1]
// LM₃ = 1×1 + 2×0 + 1×1 = 2
let g = Graph::from_edges(&[(0,1),(1,2)], false, Some(3)).unwrap();
assert_eq!(third_leap_zagreb(&g).unwrap(), 2);