leetcode——94——Binary Tree Inorder Traversal

Given a binary tree, return the inorder traversal of its nodes' values.

For example:
Given binary tree {1,#,2,3},

   1
    \
     2
    /
   3

return [1,3,2].

Note: Recursive solution is trivial, could you do it iteratively?

confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
	vector<int> res;
	vector<int> inorderTraversal(TreeNode* root) {
	    if(root == NULL)
            return res;
		if (root->left)
			inorderTraversal(root->left);
		    
		res.push_back(root->val);

		if (root->right)
			inorderTraversal(root->right);

		return res;
   
	}
};