Leetcode 145. Binary Tree Postorder Traversal二叉树后序遍历

Given a binary tree, return the postorder traversal of its nodes' values.

Example:

Input: [1,null,2,3]
   1
    \
     2
    /
   3

Output: [3,2,1]

题目链接:https://leetcode.com/problems/binary-tree-postorder-traversal/

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    
     void post_order(TreeNode* root,vector<int>&res)
    {
        if(root)
        { 
            post_order(root->left,res);
            post_order(root->right,res);
            res.emplace_back(root->val);
        }
    }

    vector<int> postorderTraversal(TreeNode* root) {
        vector<int> res;
        post_order(root,res);
        return res;
    }
};