Roman Numbers - Sorting, C#

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//Rextester.Program.Main is the entry point for your code. Don't change it.
//Compiler version 4.0.30319.17929 for Microsoft (R) .NET Framework 4.5

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text.RegularExpressions;

// aljodav
// http://rextester.com/users/376

namespace Rextester
{
    class RomanNumbersComparer:IComparer<string>{
        public int Compare(string x,string y){return ValueOf(x).CompareTo(ValueOf(y));}
        public int GetValueOf(string s){return ValueOf(s);}
        
        bool IsValidRomanNumber(string s){return true;} // I assume it is valid
        int ValueOf(char c){
            switch(c){
                case 'I':return 1;
                case 'V':return 5;
                case 'X':return 10;
                case 'L':return 50;
                case 'C':return 100;
                case 'D':return 500;
                case 'M':return 1000;
                default:throw new Exception("Invalid Roman Number.");
            }
        }
        int ValueOf(string s){
            if(IsValidRomanNumber(s)==false)throw new Exception("Invalid Roman Number");
            int acc,q,w,e;
            acc=q=w=e=0;
            
            for(int i=0;i<s.Length;++i){
                q=w;w=e;e=ValueOf(s[i]);
                if(w==0)continue;
                if(q==0){
                    if(w<e){acc+=e-w;w=e=0;}
                    else if(w>e){acc+=w;w=0;}
                }else{
                    if(q==w&&w==e){acc+=q+w+e;q=w=e=0;}
                    else if(q==w){acc+=q+w;q=w=0;}
                    else{acc+=q;}
                }
            }
            acc+=q+w+e;
            
            return acc;
        }
    }
    
    public class Program
    {
        public static void Main(string[] args)
        {
            string[] testStrings={
                "MCMXCIX",
                "MXCIX",
                "III",
                "II",
                "III", // repeated
                "I",
                "V",
                "IV",
                "XCIX",
                "MXCIX", // repeated
                "V", // repeated
                "MI"
            };
            // all strings above must be VALID roman numbers!
            
            RomanNumbersComparer rnc=new RomanNumbersComparer();
            
            Array.Sort(testStrings,rnc); // *** ATTENTION HERE! *** 
                
            foreach(string s in testStrings){
                Console.WriteLine("{0}\t\t{1}",s,rnc.GetValueOf(s));
            }
        }
    }
}

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Compilation time: 0,12 sec, absolute running time: 0,09 sec, cpu time: 0,11 sec, average memory usage: 13 Mb, average nr of threads: 3