FindDuplicatesInDirectory

Comparison.cs

using System;
using System.IO;
using System.Linq;


static bool CompareFiles(string file1, string file2)
{
    if (file1 == file2) return true; 

    
    const int BYTES = 1024 * 10;
    
    using FileStream fs1 = File.Open(file1, FileMode.Open, FileAccess.Read, FileShare.ReadWrite); 
    using FileStream fs2 = File.Open(file2, FileMode.Open, FileAccess.Read, FileShare.ReadWrite); 
    
        byte[] buffer1= new byte[BYTES]; 
        byte[] buffer2= new byte[BYTES];
    

    while (true)
    {
        int len1 = fs1.Read(buffer1, 0, BYTES);
        int len2 = fs2.Read(buffer2, 0, BYTES);

        if (!((ReadOnlySpan<Byte>)buffer1).SequenceEqual((ReadOnlySpan<byte>)buffer2)) return false; // SequenceEqual is bad.
        if (len1 == 0 || len2 == 0) break;
    }

    return true;
    
}

static void CompareInDirectory(string startingDirectory)
{

    
    var dinfo = new DirectoryInfo(startingDirectory); 
    var files = dinfo.EnumerateFiles("",SearchOption.AllDirectories)
        .Select(finfo => new { finfo.FullName, finfo.Length })
        .GroupBy(file => file.Length)
        .ToDictionary(group => group.Key, group => group.Select(file => file.FullName));
    
    foreach (var entry in files)
    {
        var bucket = entry.Value.ToArray();
        for (int i = 0; i < bucket.Length; i++) {
            for (int k = i + 1; k < bucket.Length; k++) {
                if (CompareFiles(bucket[i],bucket[k])) {
                    Console.WriteLine(bucket[i] + " and " + bucket[k] + " are the same");
                }
            }
        }
    }
}

 CompareInDirectory(@"C:\Program Files (x86)\Steam");