# My clean Morris traversal solution with C++

• ``````/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<int> postorderTraversal(TreeNode* root) {
vector<int> reval;
TreeNode dummy(0);
dummy.left = root;
root = & dummy;
while(root){
if(root->left){
TreeNode *pred(root->left);
while(pred->right && pred->right!=root){
pred = pred->right;
}
if(pred->right!=root){
//first time access current node
pred->right = root;
root = root->left;
} else {
//second time access current node
pred->right = nullptr;//revert back
backward_insert(root->left,reval);
root = root->right;
}
} else {
root = root->right;
}
}
return reval;
}
private:
void backward_insert(TreeNode* root,vector<int> & reval){
if(!root) return;
backward_insert(root->right,reval);
reval.push_back(root->val);
}
};
``````

• @yang121 This is still recursive. Yet the problem explicitly says no recursive. The traversal is basically smoke and mirrors. The core logic is the right branch recursion call of "backward_insert()".

• @ayuanx
Changed the code.

``````/**
* Definition for a binary tree node.
* struct TreeNode {
*     int val;
*     TreeNode *left;
*     TreeNode *right;
*     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<int> postorderTraversal(TreeNode* root) {
vector<int> reval;
TreeNode dummy(0);
dummy.left = root;
root = & dummy;
while(root){
if(root->left){
TreeNode *pred(root->left);
while(pred->right && pred->right!=root){
pred = pred->right;
}
if(pred->right!=root){
//first time access current node
pred->right = root;
root = root->left;
} else {
//second time access current node
pred->right = nullptr;//revert back

TreeNode *temp(root->left);
vector<int> vec;
while(temp){
vec.push_back(temp->val);
temp = temp->right;
}
reval.insert(reval.end(),vec.rbegin(),vec.rend());

root = root->right;
}
} else {
root = root->right;
}
}
return reval;
}
};
``````

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