using System;
using System.Linq;

public class Test
{
	public static void Main()
	{
		string input = " aa aaa aaaa  bb bbb bbbb cc ccc cccc cccc ";
 		var words = input.Split((char[])null, StringSplitOptions.RemoveEmptyEntries).Distinct();
 		var lookup = words.ToLookup(s => s.Length);
 		foreach (var group in lookup)
 		{
 			Console.WriteLine(string.Join(", ", group.ToArray()));
 		}
	}
}