/// <summary>
/// Time complexity: O(nlog(n)).
/// </summary>
public static IEnumerable <T> Sort(IEnumerable <T> enumerable, SortDirection sortDirection = SortDirection.Ascending)
{
//create BST
var tree = new RedBlackTree <T>();
foreach (var item in enumerable)
{
tree.Insert(item);
}
return(sortDirection == SortDirection.Ascending ?
tree.AsEnumerable() : tree.AsEnumerableDesc());
}