Given two strings `s1` and `s2`, return `true` if `s2` contains a permutation of `s1`, otherwise return `false`. In other words, return `true` if one of `s1`'s permutations is a substring of `s2`. 1.

Given a string, print all possible permutations (rearrangements) of its characters. For a string of length n, there are n! permutations.