Problem 45257. Find neighbor triangle indices

First input T is a triangulation (triplet list of indices -positive integers-, each index refering to a vertex number in a corresponding vertices list).

Given a second input t (a certain triangle row index), one would like to query the list L of all its triangle neighbor indices. A triangle is neighbor to another triangle if they share exactly one edge.

For instance if

T = [1 2 4;...
     2 3 4;...
     5 6 8;...
     6 7 8;...
     1 2 5;...
     2 5 6;...
     2 3 6;...
     3 6 7;...
     3 4 7;...
     4 7 8;...
     4 1 8;...
     1 8 5]

and t = 3, then the function should return

L = [4, 6, 12]'

since rows / (triangles of T) 4, 6, and 12 contain an edge in common with triangle / row 3.edge [6 8] for the first, edge [5 6] for the second, and edge [8 5] for the third.

Hypothesis :

- Since a triangle is not considered neighbor of itself, t should not be part of L.

- Order doesn't matter, but T must be a column vector containing all the neighbor triangle -row- indices (except itself then) once only. No duplicata is admitted.

- Edges are symmetric : [e1, e2] is the same edge as [e2, e1]

- Every indices are positive, distinct integers.