开始刷leetcode day72: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?

Java:

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