leetcode——145——Binary Tree Postorder Traversal

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

For example:

Given binary tree

{1,#,2,3}

,

1
\
2
/
3

return

[3,2,1]

.

/**
* 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> res;
vector<int> postorderTraversal(TreeNode* root) {
if(root == NULL)
return res;

if (root->left)
postorderTraversal(root->left);

if (root->right)
postorderTraversal(root->right);

res.push_back(root->val);

return res;

}
};