How does Stack Overflow generate its SEO-friendly URLs?

Question

What is a good complete regular expression or some other process that would take the title:

How do you change a title to be part of the URL like Stack

Answer 1

Here's my (slower, but fun to write) version of Jeff's code:

public static string URLFriendly(string title)
{
    char? prevRead = null,
        prevWritten = null;

    var seq = 
        from c in title
        let norm = RemapInternationalCharToAscii(char.ToLowerInvariant(c).ToString())[0]
        let keep = char.IsLetterOrDigit(norm)
        where prevRead.HasValue || keep
        let replaced = keep ? norm
            :  prevWritten != '-' ? '-'
            :  (char?)null
        where replaced != null
        let s = replaced + (prevRead == null ? ""
            : norm == '#' && "cf".Contains(prevRead.Value) ? "sharp"
            : norm == '+' ? "plus"
            : "")
        let _ = prevRead = norm
        from written in s
        let __ = prevWritten = written
        select written;

    const int maxlen = 80;  
    return string.Concat(seq.Take(maxlen)).TrimEnd('-');
}

public static string RemapInternationalCharToAscii(string text)
{
    var seq = text.Normalize(NormalizationForm.FormD)
        .Where(c => CharUnicodeInfo.GetUnicodeCategory(c) != UnicodeCategory.NonSpacingMark);

    return string.Concat(seq).Normalize(NormalizationForm.FormC);
}

My test string:

" I love C#, F#, C++, and... Crème brûlée!!! They see me codin'... they hatin'... tryin' to catch me codin' dirty... "