class Solution {

private:

    vector<vector<int> > ret;

public:

    void perm(vector<int> num,int i){

        if(i==num.size()){

            ret.push_back(num);

            return;

        }

        for(int j=i;j<num.size();j++){

            swap(num[i],num[j]);

            perm(num,i+);

            swap(num[j],num[i]);           //复原，进行下一个交换前需复原之前状态

        }

    }

    vector<vector<int> > permute(vector<int> &num) {

        perm(num,);

        return ret;

    }

};