Hello Duncan. Thanks for a good question. This is not an array of triangles, this is an array of SOME edges, in other words consider it as a set of cuts or segments. We are required to build ANY triangles by using them. The requirement of the task doesn’t ask us to keep order of these segments.

It is like they give you a box of matches and ask you to build triangles out of them. The order of the matches in the box is not important. You can mix them as you wish.