Permutations

Given an array of distinct integers, return the count of all possible orderings.

Example

Input: 1 2 3 Output: 6

Approach

At each step, pick any one of the still-unused numbers next, recurse on the rest, and count a complete permutation once every number has been placed. This branches into exactly n! leaves.

Input format

Line 1: the array, space-separated

Print the total number of permutations.