using System;

using System.Collections.Generic;

using System.Linq;

public class Program

{

    public static void Main()

    {       

        var scoringElements = new HashSet<ScoringElement> 

        {

            new ScoringElement() { Id = 1, Name = "A", Index = 0 },

            new ScoringElement() { Id = 2, Name = "B", Index = 1 },

            new ScoringElement() { Id = 3, Name = "C", Index = 2 },

            new ScoringElement() { Id = 4, Name = "D", Index = 3 }

        };

        foreach(var scoringElement in scoringElements)

        {

            Console.WriteLine(scoringElement.Name);

            Console.WriteLine(scoringElement.Index);

            Console.WriteLine();

        }

        Console.WriteLine("----------------");

        Console.WriteLine();

        var scoringElementB = scoringElements.First(s => s.Name == "B");

        scoringElements.Move(scoringElementB, 0);

        foreach(var scoringElement in scoringElements)

        {           

            Console.WriteLine(scoringElement.Name);

            Console.WriteLine(scoringElement.Index);

            Console.WriteLine();

        }

    }   

}

​

public class ScoringElement

{

    public int Id { get; set; }

    public string Name { get; set; }

    public int Index { get; set; }

}

​

public static class ScoringElementsExtensions

{

    public static void Move(this ISet<ScoringElement> scoringElements, ScoringElement scoringElement, int newIndex)

    {

        var ordered = scoringElements.OrderBy(x => x.Index).ToList();

​

        var currentIndex = scoringElement.Index;

        ordered.RemoveAt(scoringElement.Index);

        scoringElement.Index = newIndex;

        ordered.Insert(newIndex, scoringElement);

​

        if (currentIndex < newIndex)

        {

            for (int i = currentIndex; i< newIndex; i++)

            {

                ordered[i].Index--;

            }

​

        } else

        {

            for (int i = newIndex + 1; i <= currentIndex; i++)

            {

                ordered[i].Index++;

            }

        }

    }

}

​

​

​

​