589. N-ary Tree Preorder Traversal

/*
// Definition for a Node.
class Node {
public:
    int val;
    vector<Node*> children;

    Node() {}

    Node(int _val, vector<Node*> _children) {
        val = _val;
        children = _children;
    }
};
*/
class Solution {
public:
    vector<int> preorder(Node* root) {
        vector<int> ans;
        if(root == NULL){
            return ans;
        }else{
            ans.push_back(root->val);
            
            for(int i = 0; i < (root->children).size(); i++){
                vector<int> tmp = preorder(root->children[i]);
                for(int j = 0; j < tmp.size(); j++){
                    ans.push_back(tmp[j]);
                }
            }
        }
        return ans;
        
    }
};