【leetcode】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].

---

题解：用了平凡的递归方法：

/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
class Solution {
public:
    vector<int> postorderTraversal(TreeNode *root) {
        vector<int> answer;
        post(root,answer);
        return answer;
    }
    void post(TreeNode* root,vector<int>& nodes){
        if(root == NULL)
            return;
        post(root->left,nodes);
        post(root->right,nodes);
        nodes.push_back(root->val);
        return;
    }
};