Given two strings, s1 and s2, determine if s2 contains a permutation of s1. A permutation of s1 is a substring of s2 that contains the same characters with the same frequencies, but not necessarily in ...
3. DFS 做unique permutation: given input有duplicate characters。 Given a string s, return all the palindromic permutations (without duplicates) of it. Return an empty list if no palindromic permutation ...