How to create a random list of strings using recursion?

Question

I want to generate a random list of strings containing only alphanumeric characters. The length of the string can be of any size. Is there any way to do this using recursion?

Answer 1

There is no need for recursion in this. Simply write down the characters you want in your string, for example:

string allowedCharacters = "abcdefghijklmnopqrstuvwxyz0123456789";

Then you can simply grab characters from this by random:

Random rnd = new Random();
string randomString(int length)
{
    int num = allowedCharacters.Length;
    return new string(Enumerable.Range(0, length)
           .Select(i => allowedCharacters[rnd.Next(0, num)])
           .ToArray());
}

Finally, you can use this to generate a string of a random length:

// Outputs a random string of a length between 5 and 49 characters
Console.WriteLine(randomString(rnd.Next(5, 50)));

Answer 2

Since you explicitly asked for recursion, here is a recursive solution. It’s very slow, though.

static string allowedCharacters = "abcdefghijklmnopqrstuvwxyz0123456789";
static Random rnd = new Random();
static string randomString(int length)
{
    if (length == 0)
        return "";
    return allowedCharacters[rnd.Next(0, allowedCharacters.Length)]
           + randomString(length - 1);   // This is the recursive call.
}

Now you can use this to generate a string of a random length:

// Outputs a random string of a length between 5 and 49 characters
Console.WriteLine(randomString(rnd.Next(5, 50)));