46. Permutations

46. Permutations

class Solution {
public:
    /**
     * @param nums: A list of integers.
     * @return: A list of permutations.
     */
    vector<vector<int> > permute(vector<int>& nums) {
        // write your code here
        vector<vector<int>> res;
        vector<int> sub;
        vector<bool> visited(nums.size(), 0);
        if(nums.empty()){
            res.push_back(sub);//!!!!!!!!!
            return res;
        }
        helper(nums, visited, sub, res);
        return res;
    }
    
    void helper(vector<int>& nums, vector<bool> &visited, 
                vector<int> &sub, vector<vector<int>> &res){
        if(sub.size() == nums.size()){
            res.push_back(sub);
            return;
        }
        for(int i=0; i<nums.size(); i++){
            if(!visited[i]){
                sub.push_back(nums[i]);
                visited[i] = 1;
                helper(nums, visited, sub, res);
                sub.pop_back();
                visited[i] = 0;
            }
        }
    }
};