c# - A faster way of doing multiple string replacements

Question

I need to do the following:

    static string[] pats = { "?", "?", "?", "?", "?", "?", "?", "?", "?", "?" ,"è", "è", "à", "à", "ì", "ì", "?", "?", "?", "?" };
    static string[] repl = { "a", "A", "a", "A", "a", "A", "o", "O", "o", "O", "e", "E", "a", "A", "i", "I", "o", "O", "i", "I" };
    static int i = pats.Length;
    int j;

     // function for the replacement(s)
     public string DoRepl(string Inp) {
      string tmp = Inp;
        for( j = 0; j < i; j++ ) {
            tmp = Regex.Replace(tmp,pats[j],repl[j]);
        }
        return tmp.ToString();            
    }
    /* Main flow processes about 45000 lines of input */

Each line has 6 elements that go through DoRepl. Approximately 300,000 function calls. Each does 20 Regex.Replace, totalling ~6 million replaces.

Is there any more elegant way to do this in fewer passes?

Answer 1

static Dictionary<char, char> repl = new Dictionary<char, char>() { { '?', 'a' }, { '?', 'o' } }; // etc...
public string DoRepl(string Inp)
{
    var tmp = Inp.Select(c =>
    {
        char r;
        if (repl.TryGetValue(c, out r))
            return r;
        return c;
    });
    return new string(tmp.ToArray());
}

Each char is checked only once against a dictionary and replaced if found in the dictionary.