/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode() : val(0), left(nullptr), right(nullptr) {}
* TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
* TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
* };
*/
class Solution {
public:
void postOrder(TreeNode* node, vector<int> &res) {
if (node == nullptr) return;
postOrder(node->left, res);
postOrder(node->right, res);
res.push_back(node->val);
}
vector<int> postorderTraversal(TreeNode* root) {
vector<int> res;
postOrder(root, res);
return res;
}
};