Given a string s, return all the palindromic permutations (without duplicates) of it. Return an empty list if no palindromic permutation could be form. If a palindromic permutation exists, we just ...

- Note: normally 2) and 3) are in reversed order; this problem is a bit different - This is efficient when the number of characters is not limited to 26, the runtime is still O(m + n) ...