Lintcode 68 二叉树的后序遍历

/**
* Definition of TreeNode:
* class TreeNode {
* public:
*     int val;
*     TreeNode *left, *right;
*     TreeNode(int val) {
*         this->val = val;
*         this->left = this->right = NULL;
*     }
* }
*/
class Solution {
/**
* @param root: The root of binary tree.
* @return: Postorder in vector which contains node values.
*/
public:

vector<int> ans;

vector<int> postorderTraversal(TreeNode *root) {
// write your code here
if(root != NULL)
{
postorderTraversal(root->left);
postorderTraversal(root->right);
ans.push_back(root->val);
}
return ans;
}

};