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? 

/** * Definition for binary tree * struct TreeNode { *     int val; *     TreeNode *left; *     TreeNode *right; *     TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public:vector
     
       inorderTraversal(TreeNode *root) {    vector
      
        res;    if(root==NULL)return res;    TreeNode *p=root;    stack
       
         sta;    while(p!=NULL||!sta.empty())    {        while(p!=NULL)        {            sta.push(p);            p=p->left;        }        if(!sta.empty())        {            p=sta.top();            sta.pop();            res.push_back(p->val);            p=p->right;        }    }    return res;}/*void inorder(TreeNode *root, vector
        
          &res){    if(root==NULL)return;    inorder(root->left,res);    res.push_back(root->val);    inorder(root->right,res);    return;}    vector
         
           inorderTraversal(TreeNode *root) {        vector
          
            res; inorder(root,res); return res; }*/};