MergeSort

private IList<T> MergeSort(IList<T> collection)
{
    if (collection.Count <= 1)
    {
        return collection;
    }

    int middle = (collection.Count) / 2;

    IList<T> left = new List<T>();
    IList<T> right = new List<T>();

    for (int i = 0; i < middle; i++)
    {
        left.Add(collection[i]);
    }

    for (int i = middle; i < collection.Count; i++)
    {
        right.Add(collection[i]);
    }

    left = MergeSort(left);
    right = MergeSort(right);

    return Merge(left, right);
}

private IList<T> Merge(IList<T> left, IList<T> right)
{
    IList<T> collectionMerge = new List<T>();

    while (left.Count > 0 || right.Count > 0)
    {
        if (left.Count > 0 && right.Count > 0)
        {
            if (left[0].CompareTo(right[0]) <= 0)
            {
                AddFirstItemAndResizeSubCollection(collectionMerge, ref left);
            }
            else
            {
                AddFirstItemAndResizeSubCollection(collectionMerge, ref right);
            }
        }
        else if (left.Count > 0)
        {
            AddFirstItemAndResizeSubCollection(collectionMerge, ref left);
        }
        else if (right.Count > 0)
        {
            AddFirstItemAndResizeSubCollection(collectionMerge, ref right);
        }
    }

    return collectionMerge;
}

private void AddFirstItemAndResizeSubCollection(IList<T> collection, ref IList<T> subCollection)
{
    collection.Add(subCollection[0]);
    subCollection = GetRest(subCollection);
}

private IList<T> GetRest(IList<T> collection)
{
    IList<T> rest = new List<T>();

    for (int i = 1; i < collection.Count; i++)
    {
        rest.Add(collection[i]);
    }

    return rest;
}