lintcode 二叉树中序遍历

 /**
  * Definition of TreeNode:
  * class TreeNode {
  * public:
  *     int val;
  *     TreeNode *left, *right;
  *     TreeNode(int val) {
  *         this->val = val;
  *         this->left = this->right = NULL;
  *     }
  * }
  */
  //递归方法
 class Solution {
     /**
      * @param root: The root of binary tree.
      * @return: Inorder in vector which contains node values.
      */
 public:

     void inorder(TreeNode *root, vector<int> &result) {
         if (root->left != NULL) {
             inorder(root->left, result);
         }

         result.push_back(root->val);

         if (root->right != NULL) {
             inorder(root->right, result);
         }

     }

     vector<int> inorderTraversal(TreeNode *root) {
         // write your code here
         vector<int> result;
         if (root == NULL)
             return result;
         inorder(root, result);
         return result;
     }
 };