LeetCode 145. Binary Tree Postorder Traversal二叉树后序遍历 非递归

一、题目
Given a binary tree, return the Postorder traversal of its nodes’ values.

===> D E B F C A
二、演示
当时看别人的代码，刚开始怎么也看不懂，像这样拿笔在纸上多画画就明白了

三、代码实现

/*** Definition for a binary tree node.* public class TreeNode {* int val;* TreeNode left;* TreeNode right;* TreeNode(int x) { val = x; }* }*/class Solution {
    public List<Integer> postorderTraversal(TreeNode root) {
    List<Integer> result = new ArrayList<>();TreeNode node = root;Stack<TreeNode> stack=new Stack<>();if(node !=null)stack.push(node);while (!stack.isEmpty()){
    node = stack.pop();if(node.left != null){
    stack.push(node.left);}if(node.right != null){
    stack.push(node.right);}result.add(0,node.val);}return result;}
}