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题目：

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

For example:
Given binary tree {1,#,2,3},

   1
    
     2
    /
   3

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return [3,2,1].

Note: Recursive solution is trivial, could you do it iteratively?

解题思路：基础的后序遍历

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/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };www.2cto.com
 */
class Solution {
private:
    vector
  
    s;
public:
    vector
   
     postorderTraversal(TreeNode *root) { postOrder(root); return s; } void postOrder(TreeNode *root) { if (root == NULL) return; postOrder(root->left); postOrder(root->right); s.push_back(root->val); } };
   
  

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