leetcode Binary Tree Postorder Traversal 二叉树后续遍历

先给出递归版本的实现方法，有时间再弄个循环版的。代码如下：

 1 /**

 2  * Definition for binary tree

 3  * struct TreeNode {

 4  *     int val;

 5  *     TreeNode *left;

 6  *     TreeNode *right;

 7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}

 8  * };

 9  */

10 class Solution {

11 public:

12     vector<int> postorderTraversal(TreeNode *root) {

13         vector<int> nodeValues;

14         if (root == NULL) return nodeValues;

15         postorderTraversal_Rec(root,nodeValues);

16         

17         return nodeValues;

18     }

19 private:

20     

21     void postorderTraversal_Rec(TreeNode *root, vector<int>& nodeValues){

22         if (root == NULL) return;

23         if (root->left != NULL) postorderTraversal_Rec(root->left,nodeValues);

24         if (root->right != NULL)    postorderTraversal_Rec(root->right,nodeValues);

25         

26         nodeValues.push_back(root->val);

27     }

28     

29 };