后序遍历 迭代 莫里斯变换

 1 class Solution {
 2 public:
 3     vector<int> postorderTraversal(TreeNode* root) {
 4         stack<TreeNode*> s;
 5         vector<int> ans;
 6         TreeNode* temp=root;
 7         TreeNode* pre=nullptr;
 8         while(!s.empty() || temp){
 9             while(temp){
10                 s.push(temp);
11                 temp=temp->left;
12             }
13             temp=s.top();
14             s.pop();
15             if(temp->right==nullptr || temp->right==pre){
16                 ans.push_back(temp->val);
17                 pre=temp;
18                 temp=nullptr;
19             }
20             else{
21                 s.push(temp);
22                 temp=temp->right;
23             }
24         }
25         return ans;
26     }
27 };

 1 class Solution {
 2 public:
 3     void addPath(vector<int>& ans,TreeNode* root){
 4         TreeNode* temp=root;
 5         int count=0;
 6         while(temp){
 7             ans.push_back(temp->val);
 8             temp=temp->right;
 9             count++;
10         }
11         reverse(ans.end()-count,ans.end());
12     }
13     vector<int> postorderTraversal(TreeNode* root) {
14         vector<int> ans;
15         TreeNode* p=root;
16         TreeNode* q=nullptr;
17         while(p){
18             if(p->left){
19                 q=p->left;
20                 while(q->right && q->right!=p){
21                     q=q->right;
22                 }
23                 if(q->right==p){
24                     q->right=nullptr;
25                     addPath(ans,p->left); 
26                     p=p->right;
27                 }
28                 else if(q->right==nullptr){
29                     q->right=p;
30                     p=p->left;
31                 }
32             }
33             else{
34                 p=p->right;
35             }
36         }
37         addPath(ans,root);
38         return ans;
39     }
40 };