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binary-tree-postorder-traversal_2(AC).cpp
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binary-tree-postorder-traversal_2(AC).cpp
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// 2WA, 1AC, should've think more before starting coding
class Solution {
public:
vector<int> postorderTraversal(TreeNode *root) {
result.clear();
if(root == nullptr){
return result;
}
vstack.clear();
cstack.clear();
vstack.push_back(root);
cstack.push_back(0);
while(vstack.size() > 0){
if(cstack[cstack.size() - 1] == 0){
++cstack[cstack.size() - 1];
if(vstack[vstack.size() - 1]->left != nullptr){
cstack.push_back(0);
vstack.push_back(vstack[vstack.size() - 1]->left);
}
}else if(cstack[cstack.size() - 1] == 1){
++cstack[cstack.size() - 1];
if(vstack[vstack.size() - 1]->right != nullptr){
cstack.push_back(0);
vstack.push_back(vstack[vstack.size() - 1]->right);
// 1WA here, cannot push result here
// result.push_back(vstack[vstack.size() - 1]->val);
// 1WA here, cannot replace node here, this works for preorder, but not postorder
// vstack[vstack.size() - 1] = vstack[vstack.size() - 1]->right;
}
}else{
result.push_back(vstack[vstack.size() - 1]->val);
cstack.pop_back();
vstack.pop_back();
}
}
return result;
}
private:
vector<int> result;
vector<TreeNode *> vstack;
vector<int> cstack;
};