[刷题防痴呆] 0590 - N叉树的后序遍历 (N-ary T

题目地址

https://leetcode.com/problems/n-ary-tree-postorder-traversal/

题目描述

590. N-ary Tree Postorder Traversal

Given the root of an n-ary tree, return the postorder traversal of its nodes' values.

Nary-Tree input serialization is represented in their level order traversal. Each group of children is separated by the null value (See examples)

 

Example 1:


Input: root = [1,null,3,2,4,null,5,6]
Output: [5,6,3,2,4,1]
Example 2:


Input: root = [1,null,2,3,4,5,null,null,6,7,null,8,null,9,10,null,null,11,null,12,null,13,null,null,14]
Output: [2,6,14,11,7,3,12,8,4,13,9,10,5,1]

思路

• DFS.

关键点

代码

• 语言支持：Java

/*
// Definition for a Node.
class Node {
    public int val;
    public List<Node> children;

    public Node() {}

    public Node(int _val) {
        val = _val;
    }

    public Node(int _val, List<Node> _children) {
        val = _val;
        children = _children;
    }
};
*/

// dfs分治
class Solution {
    public List<Integer> postorder(Node root) {
        List<Integer> res = new ArrayList<>();
        if (root == null) {
            return res;
        }
        for (Node child: root.children) {
            res.addAll(postorder(child));
        }

        res.add(root.val);
        return res;
    }
}

// dfs遍历
class Solution {
    List<Integer> res = new ArrayList<>();
    public List<Integer> postorder(Node root) {
        traverse(root);
        return res;
    }

    private void traverse(Node node) {
        if (node == null) {
            return;
        }
        for (Node child: node.children) {
            traverse(child);
        }
        res.add(node.val);
    }
}