Linq

string[] WinningScores = new string[] {"g", "o", "g", "o", "g", "o" };
 
            var duplicates =
                   WinningScores
                       .Select((score, index) => new { score, player = index + 1 })
                       .GroupBy(x => x.score, x => x.player)
                       .Where(gxs => gxs.Count() > 1);
 
            Console.WriteLine("duplicates: {0}", duplicates.Count());  

출력 값은 2

g, o 두개가 중복되기 때문