code-shoily / yog_ex / 927f33a21f5bb0c8788e7ad075ec113bd98031fb

93%

Build Type

push

github

Committed by code-shoily

Commit Message

fix(multi): correct undirected self-loop degree counting

In standard graph theory, an undirected self-loop contributes 2 to a
node's degree. Yog.Multi.Model was counting it as 1 because the edge
ID was stored only once in out_edge_ids / in_edge_ids (MapSet.put is
idempotent).

Fixed by adding count_self_loops/2 and adding the self-loop count to
the base MapSet.size for undirected graphs in both out_degree/2 and
in_degree/2. Directed self-loops are unchanged (1 to in-degree, 1 to
out-degree, total 2).

This also fixes false-negative Eulerian path/circuit detection on
undirected multigraphs with self-loops, since Eulerian's parity checks
use Model.out_degree/2 directly.

Fixes #143

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4 existing lines in 1 file now uncovered.

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