[UVA][Math] 941 - Permutations
A permutation of a string is the set of all possible
ways to combine its characters. E.g., the permutation of "abc" is
{"abc", "acb", "bac", "bca", "cab", "cba"}. The size of this set is the
factorial of the initial string size.
Given a string S (with up to 20 characte...
