using System;

using System.Collections.Generic;

using System.Linq;

using Newtonsoft.Json;

​

public class RegionCategoryDto

{

    public string Id { get; set; }

    public string Name { get; set; }

    public string TypeId { get; set; }

    public string ParentId { get; set; }

}

​

public class RegionCategoryGraphType

{

    public string Id { get; set; }

    public string Name { get; set; }

    public RegionCategoryType CategoryType { get; set; }

    public string ParentId { get; set; }

    public string RegionName { get; set; }

    public string MarketName { get; set; }

    public bool IsAuthorizedToCurrentUser { get; set; }

    public bool IsPrimary { get; set; }

    public List<RegionCategoryGraphType> Children { get; set; } = new List<RegionCategoryGraphType>();

}

​

public enum RegionCategoryType

{

    Unknown,

    Region,

    Market,

    Group

}

​

public class TreeBuilder

{

    public static List<RegionCategoryGraphType> BuildTree(List<RegionCategoryDto> dtos)

    {

        // Step 1: Create a lookup dictionary for quick access by ID

        var lookup = dtos.ToDictionary(dto => dto.Id, dto => new RegionCategoryGraphType

        {

            Id = dto.Id,

            Name = dto.Name,

            CategoryType = MapCategoryType(dto.TypeId),

            ParentId = dto.ParentId

        });

​

        // Step 2: Identify root nodes and assign children

        var rootNodes = new List<RegionCategoryGraphType>();

​

        foreach (var node in lookup.Values)

        {

            if (string.IsNullOrEmpty(node.ParentId) || !lookup.ContainsKey(node.ParentId))

            {

                // Root node

                rootNodes.Add(node);

            }

            else

            {

                // Child node, add to parent

                var parent = lookup[node.ParentId];

                parent.Children.Add(node);

            }

        }

​

        return rootNodes;

    }

​

    private static RegionCategoryType MapCategoryType(string typeId)

    {

        return typeId switch

        {

            "1" => RegionCategoryType.Region,

            "2" => RegionCategoryType.Market,

            "3" => RegionCategoryType.Group,

            _ => RegionCategoryType.Unknown

        };

    }

}

​

// Example usage

public class Program

{

    public static void Main()

    {

        var dtos = new List<RegionCategoryDto>

        {

            new RegionCategoryDto { Id = "1", Name = "Southwesd", TypeId = "1", ParentId = null },

            new RegionCategoryDto { Id = "2", Name = "Denver", TypeId = "2", ParentId = "1" },

            new RegionCategoryDto { Id = "3", Name = "Denver South", TypeId = "3", ParentId = "2" },

            new RegionCategoryDto { Id = "4", Name = "Northeast", TypeId = "1", ParentId = null },

            new RegionCategoryDto { Id = "5", Name = "Boston North", TypeId = "2", ParentId = "4" }

        };

​

        var tree = TreeBuilder.BuildTree(dtos);

        Console.WriteLine(JsonConvert.SerializeObject(tree));

    }

​

    private static void PrintTree(List<RegionCategoryGraphType> nodes, int level)

    {

        foreach (var node in nodes)

        {

            Console.WriteLine(new string('-', level * 2) + node.Name);

            PrintTree(node.Children, level + 1);

        }

    }

}

​