145

/**
 * 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 f(TreeNode* root,vector<int>&v){
    if(root==NULL)
    return;
    f(root->left,v);
    f(root->right,v);
        v.push_back(root->val);


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