LeetCode145-Binary-Tree-Postorder-Traversal

LeetCode 145 : 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].
来源： https://leetcode.com/problems/binary-tree-postorder-traversal/

问题描述：
本题其实就是将二叉树按照后序遍历将其值保存在List中。

我的Java代码：

/** * Definition for a binary tree node. * public class TreeNode { *     int val; *     TreeNode left; *     TreeNode right; *     TreeNode(int x) { val = x; } * } */public class Solution {    private List<Integer> list ;    public List<Integer> postorderTraversal(TreeNode root) {        list = new ArrayList<Integer>();        postorder(root);        return list;    }    private void postorder(TreeNode node){        if(null==node){            return ;        }else{            postorder(node.left);            postorder(node.right);            list.add(node.val);            return ;        }    }}