二叉树的中序遍历

 1 /**
 2  * Definition of TreeNode:
 3  * class TreeNode {
 4  * public:
 5  *     int val;
 6  *     TreeNode *left, *right;
 7  *     TreeNode(int val) {
 8  *         this->val = val;
 9  *         this->left = this->right = NULL;
10  *     }
11  * }
12  */
13 class Solution {
14     /**
15      * @param root: The root of binary tree.
16      * @return: Inorder in vector which contains node values.
17      */
18 public:
19     vector<int> inorderTraversal(TreeNode *root) {
20         // write your code here
21         vector<int> order;
22         if(root == NULL)
23             return order;
24 
25         stack<TreeNode*> s;
26         TreeNode *p=root;
27         while(p!=NULL||!s.empty()) {
28             while(p!=NULL) {
29                 s.push(p);
30                 p=p->left;
31             }
32             if(!s.empty()) {
33                 p=s.top();
34                 order.push_back(p->val);
35                 s.pop();
36                 p=p->right;
37             }
38         } 
39         return order;
40     }
41 };