# 0ms c++ iterative solution

• ``````/**
* 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> a;
stack<TreeNode*> s;
vector<int> postorderTraversal(TreeNode* root) {
if (root == NULL) return a;
go (root);
return a;
}

// iterative
void go(TreeNode* t) {
s.push(t);
while(1) {
// find most left node
while (1) {
if (!s.empty() && s.top()->left &&
(a.empty() || !a.empty()  && a[a.size()-1]!=s.top()->left->val && (s.top()->right && a[a.size()-1]!=s.top()->right->val || !s.top()->right)) )
s.push(s.top()->left);
else break;
}

if (s.empty()) return;

TreeNode* mostLeft = s.top();
if (mostLeft->right && (a.empty() || !a.empty() && mostLeft->right->val != a[a.size()-1])) s.push(mostLeft->right);
else {
s.pop();
a.push_back(mostLeft->val);
}
}
}

// void go(TreeNode* t){
//     if (t == NULL) return;
//     go(t->left);
//     go(t->right);
//     a.push_back(t->val);
// }
};
``````

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