The longest sublist algorithm

Question

I\'m struggling with quite interesting assignment and looking for advice. The case is to find the longest sublist from the given list of pairs. First elements from these pai

Answer 1

Okay, a hint first.

For every pair (x, y) for a given x, you're only interested in the one with the greatest y.

For every pair (x, y) for a given y, you're only interested in the one with the smallest x.

Try building maps of respective least/greater values for the x's and y's and see where you get from there (you will need two copies of the pair list, one sorted lexicographically x -> y and one sorted lexicographically y -> x).