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;

    }

}

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

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