Binary Tree Preorder Traversal

 1 /**
 2  * Definition for binary tree
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     vector<int> preorderTraversal(TreeNode *root) {
13         
14         vector<int> vec;
15         getVal(vec, root);
16         return vec;
17     }
18     
19     void getVal(vector<int> &vec, TreeNode *root){
20         
21         if(root != NULL){
22             vec.push_back(root->val);
23             getVal(vec, root->left);
24             getVal(vec, root->right);
25         }
26     }
27 };