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There is sometimes the necessity to generate an alphanumeric key from a string, such as to generate a part of the URL based on the article title. You need to make all letters lower-case and replace some language-specific characters, as well as replace all characters other than a-z and 0-9 with a dash. What's more, no more than one dash in a row is allowed. How to solve this problem?

The most important actions are performed in the following method:

string GetKey(string text)
{
    // Replace some language-specific characters.
    Dictionary replace = new()
    {
        { 'ą', 'a' },
        { 'ć', 'c' },
        { 'ę', 'e' },
        { 'ł', 'l' },
        { 'ń', 'n' },
        { 'ó', 'o' },
        { 'ś', 's' },
        { 'ź', 'z' },
        { 'ż', 'z' }
    };
    text = text.ToLower();
    foreach ((char from, char to) in replace) { text = text.Replace(from, to); }

    // Replace all not-supported characters with dashes.
    List supported = [];
    for (char c = 'a'; c <= 'z'; c++) { supported.Add(c); }
    for (char c = '0'; c <= '9'; c++) { supported.Add(c); }
    string key = string.Empty;
    foreach (char c in text) { key += supported.Contains(c) ? c : '-'; }

    // Remove multiple dashes, as well as dashes at the beginning or end.
    key = key.Replace("--", "-");
    key = key.Trim('-');
    return key;
}

To simplify testing, the Print auxiliary method is shown below:

void Print(string text)
{
    Console.Write(text);
    Console.Write(" -> ");
    Console.WriteLine(GetKey(text));
}

A few of its calls are presented as follows:

Print("Hello world!");
Print("Dzień dobry w przepięknej Polsce! :-)");
Print("I was born on 9.11.1988.");

If you run the code, you will get the following result:

Hello world! -> hello-world
Dzień dobry w przepięknej Polsce! :-) -> dzien-dobry-w-przepieknej-polsce
I was born on 9.11.1988. -> i-was-born-on-9-11-1988

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