leetCode172|N叉树的前序遍历

import java.util.ArrayList;
import java.util.List;

public  class Preordertest4 {
    public static void main(String[] args) {
        Node node = new Node(1);
        Node node2 = new Node(3);
        Node node3 = new Node(2);
        Node node4 = new Node(4);
        Node node5 = new Node(5);
        Node node6 = new Node(6);
        List<Node> nodeList1 = new ArrayList<>();

        List<Node> nodeList2 = new ArrayList<>();
        nodeList2.add(node5);
        nodeList2.add(node6);
        nodeList1.add(node2);
        nodeList1.add(node3);
        nodeList1.add(node4);
        node2.children = nodeList2;
        node.children = nodeList1;
        List<Integer> list = preorder(node);
        System.out.println("list = " + list);
    }

    public static  List<Integer> preorder(Node root) {
        List<Integer> list = new ArrayList<>();
        if (root == null) {
            return list;
        }
        dfs(root, list);
        return list;
    }

    private static  void dfs(Node root, List<Integer> list) {
        if (root == null) {
            return;
        }
        list.add(root.val);
        if (root.children == null) {
            return;
        }
        List<Node> children = root.children;
        for (Node node : children
        ) {
            dfs(node, list);
        }
    }

    static 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;
        }
    }
}