Given a string, return all possible permutations of that string. The permutations should not include duplicates. ### Constraints: - The input string will have at most 8 characters. ### Examples: 1. Input: 'abc' Output: ['abc', 'acb', 'bac', 'bca', 'cab', 'cba'] 2. Input: 'aab' Output: ['aab', 'aba', 'baa']