Two persons each have a ranking list of n books according to their preferences. To measure how different these two preference lists are, we count the number of inversions: an inversion is a pair of books (X, Y), such that one person likes book X better than book Y while the other person likes book Y better than X. Your task is to identify an algorithm to count the number of inversion between two preference lists, with running time function grows slower than n2.

write pseudocode algorithm and show problem instance with 6 books.