LeetCode: Permutations

/// Backtracking
class Solution {
public:

    vector < vector <int> > ans;
    int ar[6 + 10];
    int n;

    void f(int l, int r){
        if(l == r){
            vector <int> cur;
            for(int i=0;i<n;i++) cur.push_back(ar[i]);
            ans.push_back(cur);
            return;
        }
        for(int i=l;i<=r;i++){
            swap(ar[l], ar[i]);
            f(l + 1, r);
            swap(ar[l], ar[i]);
        }
    }

    vector<vector<int>> permute(vector<int>& nums) {
        n = nums.size();
        for(int i=0;i<n;i++) ar[i] = nums[i];
        f(0, n-1);
        return ans;
    }
};

/// std::next_permutation
class Solution {
public:

    vector<vector<int>> permute(vector<int>& nums) {
        vector < vector <int> > ans;
        sort(nums.begin(), nums.end()); /// ***
        do{
            ans.push_back(nums);
        }while(next_permutation(nums.begin(), nums.end()));
        return ans;
    }
};