create a regular expression based on anagrams of a given string in csharp

To create a regular expression that matches anagrams of a given string, we can use the following algorithm:

1. Convert the string to a lowercase character array and sort it.
2. Iterate through each character in the sorted array and add it to a string.
3. Surround each character in the string with a character class (e.g., "[a]", "[b]", "[c]", etc.).
4. Join the character classes with "\S*" (the "non-space character" wildcard) to allow for any number of additional characters between each character.
5. Surround the entire regular expression with the word boundary metacharacters ("\b") to ensure that it matches only whole words.

Here is the implementation of the algorithm in C#:

main.cs
string CreateAnagramRegex(string word)
{
    char[] sortedWord = word.ToLower().ToCharArray();
    Array.Sort(sortedWord);
    string regexString = string.Join("", sortedWord.Select(c => $"[{c}]\\S*"));
    return $"\\b{regexString}\\b";
}
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The CreateAnagramRegex method takes a string as input and returns a regular expression as a string. Here is an example usage:

main.cs
string word = "race";
string regex = CreateAnagramRegex(word);
Console.WriteLine(regex); // Outputs "\b[a]\S*[c]\S*[e]\S*[r]\S*\b"
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This regular expression matches any string that contains the same letters as "race" (e.g., "care", "acre", "racecar", etc.).