LC.145.Post-order Traversal Of Binary Tree-优快云博客

本文介绍了一种迭代方式实现二叉树的后序遍历算法，并提供了详细的代码示例。通过此方法，可以有效地获取二叉树节点的后序遍历顺序。

https://leetcode.com/problems/binary-tree-postorder-traversal/description/

Description

Implement an iterative, post-order traversal of a given binary tree, return the list of keys of each node in the tree as it is post-order traversed.

Examples

/ \

3 8

/ \ \

1 4 11

Post-order traversal is [1, 4, 3, 11, 8, 5]

Corner Cases

What if the given binary tree is null? Return an empty list in this case.

How is the binary tree represented?

We use the level order traversal sequence with a special symbol "#" denoting the null node.

For Example:

The sequence [1, 2, 3, #, #, 4] represents the following binary tree:

/ \

2 3

/**
 * public class TreeNode {
 *   public int key;
 *   public TreeNode left;
 *   public TreeNode right;
 *   public TreeNode(int key) {
 *     this.key = key;
 *   }
 * }
 */

 1 public List<Integer> postOrder(TreeNode root) {
 2     // Write your solution here
 3     if(root == null ) return new ArrayList<Integer>() ; 
 4       List<Integer> res = new ArrayList<Integer>() ; 
 5     traverse(root, res) ; 
 6     return res ; 
 7   }
 8   private void traverse(TreeNode root, List<Integer> res){
 9       //base case 
10     if(root == null ) return ; 
11     traverse(root.left, res); 
12     traverse(root.right, res) ; 
13     res.add(root.key); 
14   }