LeetCode 589. N叉树的前序遍历(N-ary Tree Preorder Traversal)

589. N叉树的前序遍历

589. N-ary Tree Preorder Traversal

LeetCode589. N-ary Tree Preorder Traversal

题目描述

给定一个 N 叉树，返回其节点值的前序遍历。

例如，给定一个 3 叉树 :

返回其前序遍历: [1,3,5,6,2,4]。

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> preorder(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();

            if (node.children != null) {

                for (int i = node.children.size() - 1; i >= 0; i--) {

                    stack.push(node.children.get(i));

                }

            }

            result.add(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> preorder(Node root) {

        if (root == null) {

            return result;

        }

        result.add(root.val);

        List<Node> node = root.children;

        for (int i = 0; i < node.size(); i++) {

            preorder(node.get(i));

        }

        return result;

    }

}

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LeetCode 589. N叉树的前序遍历(N-ary Tree Preorder Traversal)

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