LeetCode No145 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?

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题目链接：https://leetcode.com/problems/binary-tree-postorder-traversal/

题目大意：求一个二叉树的后续遍历。

思路：递归。

附上代码：

/**
* 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> ans ;
if ( root == NULL )
return ans ;
postOrder ( root, ans ) ;
return ans ;
}
void postOrder ( TreeNode* root , vector <int>& ans )
{
if ( root == NULL )
return ;
postOrder ( root -> left , ans ) ;
postOrder ( root -> right , ans ) ;
ans.push_back ( root -> val ) ;
}
};