QSort.cs

using System.Collections.Generic;

namespace WPF.Common.Helpers
{
    public delegate int ItemComparer<in T>(T a, T b);
    public delegate void Swap<T>(IList<T> elements, int index1, int index2);
    public static class QSort
    {

        public static void Sort<T>(IList<T> elements, ItemComparer<T> comparer, bool reverse = false)
        {
            Sort(elements, CollectionSwap, comparer, reverse);
        }
        public static void Sort<T>(IList<T> elements, Swap<T> swap, ItemComparer<T> comparer, bool reverse = false)
        {
            Sort(elements, 0, elements.Count - 1, swap, comparer);
            if (reverse)
                for (int i = 0; i < elements.Count / 2; i++)
                    swap(elements, i, elements.Count - 1 - i);
        }

        static void Sort<T>(IList<T> elements, int left, int right, Swap<T> swap, ItemComparer<T> comparer)
        {
            if (elements.Count == 0)
                return;
            int i = left;
            int j = right;
            T pivot = elements[(left + right) / 2];
            while (i <= j)
            {
                while (comparer(elements[i], pivot) < 0)
                    i++;
                while (comparer(elements[j], pivot) > 0)
                    j--;
                if (i <= j)
                {
                    swap(elements, i, j);
                    i++;
                    j--;
                }
            }
            if (left < j)
                Sort(elements, left, j, swap, comparer);
            if (i < right)
                Sort(elements, i, right, swap, comparer);
        }
        static void CollectionSwap<T>(IList<T> elements, int index1, int index2)
        {
            T tmp = elements[index1];
            elements[index1] = elements[index2];
            elements[index2] = tmp;
        }
    }
}