using static System.Console;

using System.Collections.Generic;

​

public static class Sorteio {

    public static void Main() {

        int[] array = { 1, 2, 3, 4 };

        array.Shuffle();

        foreach (var valor in array) WriteLine(valor);

        WriteLine("Soma: {0}", array[0] + array[2]); // soma 1o. e 3o. elemento

        //vamos de novo

        array.Shuffle(); //com poucos númros tem chance de repetir

        WriteLine($"Soma novo sorteio: {array[0] + array[2]}"); // soma 1o. e 3o. elemento

    }

}

​

namespace System.Collections.Generic {

    public static class IListExt {

        static Random r = new Random(DateTime.Now.Millisecond);

​

        public static void Shuffle<T>(this IList<T> list, int lowerItem, int upperItem) {

            upperItem = upperItem > list.Count ? list.Count : upperItem;

            lowerItem = lowerItem < 0 ? 0 : lowerItem;

            for (int i = lowerItem; i < upperItem; i++) {

                int j = r.Next(i, upperItem);

                T tmp = list[j];

                list[j] = list[i];

                list[i] = tmp;

            }

        }

​

        public static void Shuffle<T>(this IList<T> list, int upperItem) => list.Shuffle(0, upperItem);

​

        public static void Shuffle<T>(this IList<T> list) => list.Shuffle(0, list.Count);

    }

}