Scramble & descramble text

Question

I already got this method to scramble my text but I have no clue on how to unscramble it.

string input = "https://www.google.de/";
char[] chars = input.ToArray();
Random r = new Random(259);
for (int i = 0; i < chars.Length; i++)
{
    int randomIndex = r.Next(0, chars.Length);
    char temp = chars[randomIndex];
    chars[randomIndex] = chars[i];
    chars[i] = temp;
}
new string(chars);

Console.WriteLine(chars);
Console.ReadKey();

How can I make a scramble or shuffle function that shuffles the text with a specific number so it scrambles the text the same way every time and how can I unshuffle it after that?

Answer 1

Just do the same thing you already did backwards (you need to use the same random numbers from the same seed in reverse order, so get those in a list first):

        string input = "https://www.google.de/";
        char[] chars = input.ToArray();
        Random r = new Random(259);
        for (int i = 0; i < chars.Length; i++)
        {
            int randomIndex = r.Next(0, chars.Length);
            char temp = chars[randomIndex];
            chars[randomIndex] = chars[i];
            chars[i] = temp;
        }
        string scrambled = new string(chars);

        Console.WriteLine(chars);
        Console.ReadKey();

        r = new Random(259);
        char[] scramChars = scrambled.ToArray();
        List<int> swaps = new List<int>();
        for (int i = 0; i < scramChars.Length; i++)
        {
            swaps.Add(r.Next(0, scramChars.Length));
        }
        for (int i = scramChars.Length - 1; i >= 0; i--)
        {
            char temp = scramChars[swaps[i]];
            scramChars[swaps[i]] = scramChars[i];
            scramChars[i] = temp;
        }

        string unscrambled = new string(scramChars);

        Console.WriteLine(scramChars);