using System;
// In a combination, the subset elements can be listed in any order.
public class TwoLettersCombinationFromABCD_CSharp
{
private static void create_2_letters_combination(char[] letters) {
int size = letters.Length;
for (int i = 0; i < size; i++) {
for (int j = i + 1; j < size; j++) {
Console.WriteLine("{0}{1}", letters[i], letters[j]);
}
}
}
public static void Main(string[] args)
{
char[] letters = new char[] {'A', 'B', 'C', 'D'};
create_2_letters_combination(letters);
}
}
/*
run:
AB
AC
AD
BC
BD
CD
*/