Algorithm to generate all combinations of a specific size from a single set

Question

I am looking for solution in c# to generate combinations on given list of characters or word to perform dictionary attack on zip files. because we lost passwords file for those zip. Advantage is that we know possible words on it. Dictionary should contain all the combos of words that I choose. And all characters/words are small case only.

Example: Let say we have a set of chars:

Set A = {A,B,C}

A,B,C   =3

AA,AB,AC

BA,BB,BC

CA,CB,CC    =9


AAA,AAB,AAC,ABA,ABB,ABC,ACA,ACB,ACC

BAA,BAB,BAC,BBA,BBB,BBC,BCA,BCB,BCC

CAA,CAB,CAC,CBA,CBB,CBC,CCA,CCB,CCA    = 27


TOTAL POSIBLE COMBINATION 39

from the list of words a single word/character may repeat maximum of 4 times. If any such alogrithm/logic available please suggest.

Answer 1

Here is a C# implementation using recursion:

static char[] A={'a','b','c'};
static int N = 3;
static void foo(string s)
{
    if (s.Length == N)
    {
        Console.WriteLine(s);
        return;
    }
    for (int i = 0; i < A.Length; i++)
    {
        string t = s;
        t += A[i];
        foo(t);
    }
}

Demo

If you want to retrieve the values later, store the strings in a global array before returning from function foo().