TH - Đếm trùng

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
using System.IO;

namespace func
{
    class Program
    {
        static void Main(string[] args)
        {
            const string fileInput = "../../input.txt";
            const string fileOutput = "../../output.txt";

            int[] inp = readFile(fileInput);

            int dapan = task(inp);

            writeFile(fileOutput, dapan.ToString());

        }

        public static int task(int[] a)
        {
            int total = 0;
            int[] temp = new int[findMax(a) + 1];
            foreach(int value in a)
            {
                temp[value]++;
            }
            foreach (int value in temp)
            {
                if (value >= 2) total += value;
            }

            return total;

        }

        public static int findMax(int[] a)
        {
            int max = a[0];
            for (int i = 1; i < a.Length; i++)
            {
                max = Math.Max(a[i], max);
            }
            return max;
        }

        public static int[] readFile(string path)
        {

            FileStream fs = new FileStream(path, FileMode.Open);
            StreamReader sReader = new StreamReader(fs, Encoding.UTF8);
            int n = int.Parse(sReader.ReadLine());
            int[] res = new int[n];
            string[] temp = sReader.ReadLine().Split(' ');
            for (int i = 0; i < n; i++)
            {
                res[i] = int.Parse(temp[i]);
            }
            sReader.Close();
            fs.Close();
            Console.WriteLine("Doc file thanh cong !");
            return res;

        }

        public static void writeFile(string path, string data)
        {

            FileStream fsW = new FileStream(path, FileMode.Create);
            StreamWriter sWriter = new StreamWriter(fsW, Encoding.Unicode);
            sWriter.Write(data);
            sWriter.Flush();
            fsW.Close();
            fsW.Close();
            Console.WriteLine("Ghi file thanh cong !");
        }
    }
}