Roman Numbers, Sorting through IComparer, 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
{
    using RomanNumbersComparer=Rextester.Program;
    class Program:IComparer<string>
    {
        public static void Main(string[] args)
        {
            string[] romanNumbers={
                "MCMXCIX",
                "MXCIX",
                "III",
                "II",
                "III", // repeated
                "I",
                "X",
                "V",
                "IV",
                "XCIX",
                "MXCIX",
                "VI",
                "IX",
                "MI",
                "I", // repeated
                "XXXI",
                "XXX",
                "LI",
                "VIII",
                "VII",
            };
            // all strings must be VALID roman numbers
            
            RomanNumbersComparer rnc=new RomanNumbersComparer();
            
            Array.Sort(romanNumbers,rnc);
            Array.ForEach(romanNumbers,s=>Console.WriteLine("{0}\t\t{1}",s,rnc.GetValueOf(s)));
        }
        
        public int Compare(string x,string y){return _valueOf(x).CompareTo(_valueOf(y));}
        public int GetValueOf(string x){return _valueOf(x);}
        
        Func<string,int> _valueOf=s=>{
            Func<char,int> _valueOf=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("Número Romano Inválido.");}};
            int q=0,w=0,e=0,a=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){a+=e-w;w=e=0;}else if(w>e){a+=w;w=0;}
                }else{
                    if(q==w&&w==e){a+=q+w+e;q=w=e=0;}else if(q==w){a+=q+w;q=w=0;}else{a+=q;}
                }
            }
            return a+q+w+e;
        };
    }
}

Show compiler warnings [ + ] Show input
Compilation time: 0,12 sec, absolute running time: 0,09 sec, cpu time: 0,08 sec, average memory usage: 17 Mb, average nr of threads: 3