binary-tree-inorder-traversal——二叉树中序遍历

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

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

   1
    \
     2
    /
   3

return[1,3,2].

 /**
  * 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;
     }

 };