DuplicateFinder/Program.cs

using System;
using System.Collections.Generic;
using System.IO;
using System.Linq;
using System.Security.Cryptography;

namespace DuplicateFinder
{
    internal class Program
    {
        private static string CalculateSha1(string filePath)
        {
            using (var sha1 = SHA1.Create())
            {
                using (var stream = File.OpenRead(filePath))
                {
                    byte[] hashBytes = sha1.ComputeHash(stream);
                    return BitConverter.ToString(hashBytes).Replace("-", "").ToLower();
                }
            }
        }

        static void Main(string[] args)
        {
            Console.Write("Enter directory path: ");
            string directoryPath = Console.ReadLine();

            Dictionary<string, List<string>> fileHashes = new Dictionary<string, List<string>>();

            foreach (string filePath in Directory.EnumerateFiles(directoryPath, "*.*", SearchOption.AllDirectories))
            {
                string hash = CalculateSha1(filePath);

                if (fileHashes.ContainsKey(hash))
                {
                    fileHashes[hash].Add(filePath);
                }
                else
                {
                    fileHashes[hash] = new List<string> { filePath };
                }
            }

            Console.WriteLine("\nDuplicate files:");
            foreach (var group in fileHashes.Values.Where(v => v.Count > 1))
            {
                foreach (var filePath in group)
                {
                    Console.WriteLine(filePath);
                }
                Console.WriteLine();
            }

            Console.ReadKey();
        }
    }
}