Neighbor Polygons from List of Polygon Indices

Question

I have a mesh in a form like this. with a list of indices representing each polygon at the end. I need to generate a list of neighboring polygons for each polygon, and was w

Answer 1

Without precomputed data it is not possible to do it faster than looping through all faces.

For precomputed data it is enough for each vertex to hold a list of faces where it is used. Finding neighbors is done with intersecting face lists of 2 vertices.