Permutations

class Solution {
public:
    void dfs(vector<vector<int> > &res, int pos, vector<int> &num) {
        if (pos==num.size()-1) {
            res.push_back(num);
        }
        for (int i=pos; i<num.size(); i++) {
            int temp=num[pos];
            num[pos]=num[i];
            num[i]=temp;
            
            dfs(res,pos+1,num);
            num[i]=num[pos];
            num[pos]=temp;
            
        }
        
    }
    vector<vector<int> > permute(vector<int> &num) {
        vector<vector<int> > res;
        if (num.size()==0) return res;
        dfs (res, 0, num);
        return res;
    }
};

II:

class Solution {
public:
    bool isSame(int pos, int cur, vector<int> &num) {
        for (int i=pos; i<cur; i++) {
            if (num[i]==num[cur]) return true;
        }
        return false;
    }
    void dfs(vector<vector<int> > &res, int pos, vector<int> &num) {
        if (pos==num.size()-1) res.push_back(num);
        for (int i=pos; i<num.size(); i++)  {
            if (!isSame(pos, i, num)) {
                int temp=num[pos];
                num[pos]=num[i];
                num[i]=temp;
                dfs(res,pos+1,num);
                num[i]=num[pos];
                num[pos]=temp;
            }
        }
    }
    
    vector<vector<int> > permuteUnique(vector<int> &num) {
        vector<vector<int> > res;
        if (num.size()==0) return res;
        dfs(res,0,num);
        return res;
    }
};