Problem 45220. Find triangles from edge

First input is T, a Triplet list of indices -whom each row actually contains the three indices of a triangle vertices-. size(T) = [nb_triangles, 3]. Second input is e = [e1, e2], a row vector, couple of indices. Output S is the triplet list of indices which Share the edge e. For instance, if
e = [2, 4]
and T a tetrahedron
T = [1, 2, 3;...
1, 3, 4;...
1, 2, 4;...
2, 3, 4]
then the output of the function is
S = [1, 2, 4;...
2, 3, 4]
since both triangles [1, 2, 4] and [2, 3, 4] contain the edge [2, 4].
Conditions :
  • If the edge is not part of any triangle in the list, the function must of course return the empty set, [].
  • Edges are symmetric : [e1, e2] is the same edge as [e2, e1]
  • Order of rows / edges in the output doesn't matter.
  • Triangle indices are assumed always to be sorted in ascending order, T = [t1, t2, t3] with t1 < t2 < t3.
  • Every indices are positive, distinct integers.
See also
Solve

Solution Stats

60.0% Correct | 40.0% Incorrect
Last Solution submitted on Nov 16, 2025

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