using System;

using System.Xml;

using System.Collections;

​

public class Program

{

    public static void Main()

    {

        XmlDocument doc = new XmlDocument( );

​

        //(1) the xml declaration is recommended, but not mandatory

        XmlDeclaration xmlDeclaration = doc.CreateXmlDeclaration( "1.0", "UTF-8", null );

        XmlElement root = doc.DocumentElement;

        doc.InsertBefore( xmlDeclaration, root );

​

        //(2) string.Empty makes cleaner code

        XmlElement body = doc.CreateElement( string.Empty, "body", string.Empty );

        doc.AppendChild( body );

​

        XmlElement l1_1 = doc.CreateElement( string.Empty, "level1", string.Empty );

        body.AppendChild( l1_1 );

​

        XmlElement l2_1 = doc.CreateElement( string.Empty, "level2", string.Empty );

        XmlText text1 = doc.CreateTextNode( "text 1" );

        l2_1.AppendChild( text1 );

        l1_1.AppendChild( l2_1 );

​

        XmlElement l2_2 = doc.CreateElement( string.Empty, "level2", string.Empty );

        XmlText text2 = doc.CreateTextNode( "other text 2" );

        l2_2.AppendChild( text2 );

        l1_1.AppendChild( l2_2 );

​

        XmlElement l1_2 = doc.CreateElement( string.Empty, "level1", string.Empty );

        body.AppendChild( l1_2 );

​

        XmlElement l2_3 = doc.CreateElement( string.Empty, "level2", string.Empty );

        XmlText text3 = doc.CreateTextNode( "text 3" );

        l2_3.AppendChild( text3 );

        l1_2.AppendChild( l2_3 );

​

        XmlElement l2_4 = doc.CreateElement( string.Empty, "level2", string.Empty );

        XmlText text4 = doc.CreateTextNode( "other text 4" );

        l2_4.AppendChild( text4 );

        l1_2.AppendChild( l2_4 );

        XmlNode node = doc.DocumentElement;

        listNode(node, 0);

​

        Console.WriteLine("OK:" + (getNearestParent(text3, text4) == l1_2).ToString());

    }

    public static void listNode(XmlNode node, int level) {

        Console.WriteLine( pad(level) + node.Name);

        int nextlevel = level + 1;

        foreach (XmlNode child in node.ChildNodes) {

            listNode(child, nextlevel );    

        }

​

        /*lNode child2;

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

            child2 = node.ChildNodes[i];

            listNode(child2, nextlevel);

        }*/

    }

    public static string pad(int level) {

        System.Text.StringBuilder sb = new System.Text.StringBuilder();

        while (level-- != -1) {

            sb.Append("   ");

        }

        return sb.ToString();

    }

    public static XmlNode getNearestParent(XmlNode n1, XmlNode n2) {

        ArrayList parents = new ArrayList();

        XmlNode current;

        //getting all parents of n1

        current = n1;

        while (current.ParentNode != null) {

            parents.Add(current.ParentNode);

            current = current.ParentNode;

        }

​

        //checking which of the parents of n2 is in parents of n1

        current = n2;

        while (current.ParentNode != null) {

            if (parents.IndexOf(current) >= 0) 

                return current;

            current = current.ParentNode;

        }

        return null;

    }

}