LeetCode 46. Permutations

class Solution {
public:
    vector<vector<int>> res;
    
    vector<vector<int>> permute(vector<int>& nums) {
        vector<int> cur;
        vector<bool> used(nums.size());
        dfs(cur,used,nums);
        return res;
    }
    
    void dfs(vector<int> cur, vector<bool> &used, vector<int>& nums){
        if (cur.size()==nums.size()){
            res.push_back(cur);
            return;
        }
        for (int i=0;i<nums.size();++i){
            if (used[i]) continue;
            used[i]=true; cur.push_back(nums[i]);
            dfs(cur,used,nums);
            used[i]=false; cur.pop_back();
        }    
    }
};

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