using System;

using System.Linq;

using System.Collections.Generic;

using System.Xml;

using System.Xml.Serialization;

using System.IO;

public class Program

{

    public static void Main()

    {

        string xmlData = @"<?xml version=""1.0"" encoding=""UTF-8""?>

                <nodes>

                    <node>

                        <id>1</id>

                    </node>

                    <node>

                        <id>2</id>

                        <dependency>1</dependency>

                    </node>

                    <node>

                        <id>3</id>

                        <dependency>2</dependency>

                    </node>

                    <node>

                        <id>4</id>

                    </node>

                    <node>

                        <id>5</id>

                        <dependency>4</dependency>

                    </node>

                    <node>

                        <id>6</id>

                        <dependency>2</dependency>

                        <dependency>5</dependency>

                    </node>

                </nodes>";

​

            var serializer = new XmlSerializer(typeof(Nodes));

            Nodes result;

​

            using (TextReader reader = new StringReader(xmlData))

            {

                result = (Nodes)serializer.Deserialize(reader);

            }

​

            Parse(result,6).Dump();

    }

    public static IEnumerable<int> Parse(Nodes source,int Id)

    {

        var node = source.Node.First(x=>x.Id == Id);

        yield return node.Id;

        foreach(var d in node.Dependency)

        {

            foreach(var item in Parse(source,d))

                yield return item;

        }

​

    }

}

​

[XmlRoot(ElementName="node")]

    public class Node 

    {

        [XmlElement(ElementName="id")]

        public int Id { get; set; }

        [XmlElement(ElementName="dependency")]

        public List<int> Dependency { get; set; }

    }

​

    [XmlRoot(ElementName="nodes")]

    public class Nodes 

    {

        [XmlElement(ElementName="node")]

        public List<Node> Node { get; set; }

    }