Write a method to compute all permutations of a string whose charac ters are not necessarily unique. The list of permutations should not have duplicates.
Example1:
Input: S = "qqe" Output: ["eqq","qeq","qqe"]
Example2:
Input: S = "ab" Output: ["ab", "ba"]
Note:
- All characters are English letters.
1 <= S.length <= 9