solution.cpp

/**
 * 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) {}
 * };
*/
classSolution {
public:
 vector<int> postorderTraversal(TreeNode* root) {
 vector<int> ans;
f(root, ans);
return ans;
 }

private:
voidf(TreeNode *root, vector<int> &ans) {
if(!root)
return;

f(root->left, ans);
f(root->right, ans);
 ans.push_back(root->val);
 }
};