using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace DOAN.Common
{
  

    public class Node
    {
        public int Id { get; set; }
        public int? ParentId { get; set; }
    }

    public static class TreeNodeHelper
    {
        /// <summary>
        /// 获取指定节点的所有后代节点。
        /// </summary>
        /// <param name="nodes">所有节点的集合。</param>
        /// <param name="rootId">根节点的 ID。</param>
        /// <returns>所有后代节点的列表。</returns>
        public static List<Node> GetDescendants(List<Node> nodes, int rootId)
        {
            var descendants = new List<Node>();

            void FindChildren(Node node)
            {
                var children = nodes.Where(n => n.ParentId == node.Id).ToList();
                foreach (var child in children)
                {
                    descendants.Add(child);
                    FindChildren(child);
                }
            }

            var rootNode = nodes.FirstOrDefault(n => n.Id == rootId);
            if (rootNode != null)
            {
                FindChildren(rootNode);
            }

            return descendants;
        }
    }
}