0145-binary-tree-postorder-traversal.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) {}
 * };
 */
class Solution {
public:

    void postorder(TreeNode* root, vector<int>& arr){

    if(root==NULL){
        return;
    }

    postorder(root->left, arr);
    postorder(root->right, arr);
    arr.push_back(root->val);
}

    vector<int> postorderTraversal(TreeNode* root) {

        vector<int> ans;
        postorder(root,ans);
        return ans;
        
    }
};