LeetCode题解之 Binary Tree Preorder Traversal

 1 vector<int> preorderTraversal(TreeNode* root) {
 2        vector<int> v;
 3         preBorder(root, v);
 4         return v;
 5     }
 6     
 7     void preBorder(TreeNode *root, vector<int> &v)
 8     {
 9         if (root == NULL)
10             return ;
11         v.push_back(root->val);
12         preBorder(root->left, v);
13         preBorder(root->right, v);
14     }