LeetCode 145. 二叉树的后序遍历（Binary Tree Postorder Traversal）

 1 /**
 2  * Definition for a binary tree node.
 3  * struct TreeNode {
 4  *     int val;
 5  *     TreeNode *left;
 6  *     TreeNode *right;
 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 8  * };
 9  */
10 class Solution {
11 public:
12     vector<int> postorderTraversal(TreeNode* root) {
13         vector<int> res;
14         TreeNode* node = root, *pre = NULL;
15         stack<TreeNode*> s;
16         while(node || s.size()){
17             while(node){
18                 s.push(node);
19                 node = node->left;
20             }
21             node = s.top();
22             if(node->right && node->right != pre)
23                 node = node->right;
24             else{
25                 res.push_back(node->val);
26                 s.pop();
27                 pre = node;
28                 node = NULL;
29             }
30         }
31         return res;
32     }
33 };