/**

  * 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<int> inorderTraversal(TreeNode *root) {

         vector<int> res;

         if(root==NULL) return res;

         stack<TreeNode*> s;

         TreeNode* cur=root;

         while(cur||!s.empty()){

             while(cur!=NULL){

                 s.push(cur);

                 cur=cur->left;

             }

             cur=s.top();

             s.pop();

             res.push_back(cur->val);

             cur=cur->right;

         }

         return res;

     }

 };