剑指offer:字符串的排列
class Solution {
public:
    vector<string> Permutation(string str) {
        if(str.empty())
            return {};
        sort(str.begin(),str.end());
        vector<string> answer;
        answer.push_back(str);
        while(next_permutation(str.begin(),str.end()))
        {
            answer.push_back(str);
        }
        return answer; 
    }
};