【二叉树】后序遍历【Add to List 145. Binary Tree Postorder Traversal】

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

/** * 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:    vector<int> ans;    //  后序遍历 -> 左右根    vector<int> postorderTraversal(TreeNode* root) {        getPostOrder(root);        return ans;    }    void getPostOrder(TreeNode* root){        if(root==NULL) return;        getPostOrder(root->left);        getPostOrder(root->right);        ans.push_back(root->val);        return;    }};