LeetCode 590. N叉树的后序遍历(N-ary Tree Postorder Traversal)

590. N叉树的后序遍历
590. N-ary Tree Postorder Traversal

题目描述
给定一个 N 叉树，返回其节点值的后序遍历。

LeetCode590. N-ary Tree Postorder Traversal

例如，给定一个 3 叉树:

返回其后序遍历: [5,6,3,2,4,1].

说明: 递归法很简单，你可以使用迭代法完成此题吗?

Java 实现
Iterative Solution

import java.util.LinkedList;
import java.util.List;
import java.util.Stack;

class Node {
    public int val;
    public List<Node> children;

    public Node() {
    }

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

class Solution {
    public List<Integer> postorder(Node root) {
        List<Integer> result = new LinkedList<>();
        if (root == null) {
            return result;
        }
        Stack<Node> stack = new Stack<>();
        stack.push(root);
        while (!stack.isEmpty()) {
            Node node = stack.pop();
            for (Node child:node.children){
                stack.push(child);
            }
            result.add(0, node.val);
        }
        return result;
    }
}

Recursive Solution

import java.util.LinkedList;
import java.util.List;

class Node {
    public int val;
    public List<Node> children;

    public Node() {
    }

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

class Solution {
    List<Integer> result = new LinkedList<>();

    public List<Integer> postorder(Node root) {
        if (root == null) {
            return result;
        }
        List<Node> node = root.children;
        for (int i = 0; i < node.size(); i++) {
            postorder(node.get(i));
        }
        result.add(root.val);
        return result;
    }
}

相似题目

• 144. 二叉树的前序遍历
• 429. N叉树的层序遍历
• 590. N叉树的后序遍历

参考资料

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