Perplexity of Permutations

A permutation of N integers from 1 to N is an array where each number has appeared exactly once in the array. The array [1,3,2,5,4] is a permutation of 5 numbers. For any array of size N, there are N factorial permutations in total.


This is a companion discussion topic for the original entry at https://toph.co/p/perplexity-of-permutations