using System;
using System.Linq;
class Program
{
static void Main(string[] args)
{
var letters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ".ToCharArray();
var sequence = from one in letters
from two in letters
from three in letters
from four in letters
orderby one, two, three, four
select new string(new[] { one, two, three, four });
foreach (var s in sequence.Take(20)) {
Console.WriteLine(s);
}
Console.WriteLine("...");
Console.WriteLine("Total sequence size: " + sequence.Count());
}
}
/*
run:
AAAA
AAAB
AAAC
AAAD
AAAE
AAAF
AAAG
AAAH
AAAI
AAAJ
AAAK
AAAL
AAAM
AAAN
AAAO
AAAP
AAAQ
AAAR
AAAS
AAAT
...
Total sequence size: 456976
*/