next_permutation真香

class Solution {
public:
    int a[15];
    vector<string> Permutation(string str) {
        vector<string>res;
        memset(a,0,sizeof a);
        int n=str.size();
        for(int i=0;i<n;i++){
            a[i]=str[i]-'a';
        }
        do{
            string t;
            for(int i=0;i<n;i++)
                  t+=a[i]+'a';
            res.emplace_back(t);
        }while(next_permutation(a,a+n));
        return res;
    }
};