[leetcode]Binary Tree Postorder Traversal

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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?

演算法思路：

最簡單的後序遍曆。不解釋了。

代碼如下：

 1 public class Solution { 2     List<Integer> res = new ArrayList<Integer>(); 3     public List<Integer> postorderTraversal(TreeNode root) { 4         if(root == null) return res; 5         if(root.left != null) postorderTraversal(root.left); 6         if(root.right != null) postorderTraversal(root.right); 7         res.add(root.val); 8         return res; 9     }10 }