AlphabeticalRank, 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;

namespace Rextester
{
    public class Program
    {
        public static void Main(string[] args)
        {   
            var testArray = new []{ "DACB", "CA", "FLCR", "RTZX" };

foreach (var test in testArray)
            {
                Console.WriteLine("Alphabetical rank of \"{0}\": {1}", test, AlphabeticalRank(test));
            }
        }

public static int AlphabeticalRank(string s)
        {
            var rankingArray = new List<char>(s.ToCharArray());
            rankingArray.Sort();
            var score = 1; //this is the lowest possible rank

for(int i = 0; i < s.Length -1; i++){

var rank = rankingArray.IndexOf(s[i]);
                score += Factorial(rank) * rank;

rankingArray.RemoveAt(rank);
            }

return score;
        }

public static int Factorial(int n)
        {
            var product = 1; 
            for (int i = n; i > 0; i--)
            {
                product *= i;
            }

return product;
        }
    }
}

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Compilation time: 0,14 sec, absolute running time: 0,09 sec, cpu time: 0,09 sec, average memory usage: 14 Mb, average nr of threads: 3, absolute service time: 0,26 sec