And this is effectively a list of tuples rather than a real 2d list of non-constant dimensions.

seriously...? :/

I answer your question in the most informative way and you downvote me...? :o

This "horribly dying" is about your algorithm and the fact that it IS especially inefficient compared to this one. That's just a fact and a valuable information, don't take it so personally... :/

errr... this solution is the best you can do for that kind of problem... x)

for instance, your solution is horribly dying against huge inputs with huge ranges, compared to the present one. ;)