[LeetCode]Binary Tree Postorder Traversal

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].

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

迭代的方法略显复杂。

递归的方法很统一。先序，中序，后续，只要修改遍历的顺序即可。

/**
 * 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> postorderTraversal(TreeNode* root) {
        vector<int> result;
        traversal(root,result);
        return result;
    }
    void traversal(TreeNode* root,vector<int>& ret)
    {
        if(root)
        {
            traversal(root->left,ret);
            traversal(root->right,ret);
            ret.push_back(root->val);
        }
    }
};