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

For example:

1    \     2    /   3

return [1,3,2].

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

confused what "{1,#,2,3}" means? 

非递归思路：

递归代码：

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; *///中序遍历：左根右class Solution {public:     vector
   
     res;    vector
    
      inorderTraversal(TreeNode *root) {                    if (!root)             return res;            inorderTraversal(root->left);        res.push_back(root->val);            inorderTraversal(root->right);        return res;    }};