Program.cs

IList<FileInfo> fileInfos =
      new DirectoryInfo( "/path/to/reference/source/directory" )
            .GetFiles( "*.cs" )
            .ToList( );

Console.WriteLine( $"found {fileInfos.Count} cs files" );

int globalAllmanCount = 0;
int globalKAndRCount = 0;
int globalMixedCount = 0;

void UpdateStats( int allmanCount, int kAndRCount ) {
   if( allmanCount+kAndRCount == 0 )
      return;

   float kAndRPercent = kAndRCount*100f/( allmanCount+kAndRCount );
   if( kAndRPercent <= .1f )
      ++globalAllmanCount;
   else if( kAndRCount >= .9f )
      ++globalKAndRCount;
   else
      ++globalMixedCount;
}

async Task ScanFile( FileInfo fi ) {
   using StreamReader sr = new(fi.OpenRead( ));
   string line;
   int allmanCount = 0;
   int kAndRCount = 0;
   while( ( line = await sr.ReadLineAsync( ) ) != null ) {
      if( !line.Contains( '{' ) )
         continue;

      if( string.IsNullOrWhiteSpace( line.Split( '{' )[ 0 ] ) )
         ++allmanCount;
      else
         ++kAndRCount;
   }

   UpdateStats( allmanCount, kAndRCount );
}

int cnt = 0;
foreach( FileInfo fi in fileInfos ) {
   await ScanFile( fi );
   ++cnt;
   Console.Write( $"\rscanned {cnt}/{fileInfos.Count} files {cnt*100f/fileInfos.Count:0.00}%" );
}

Console.WriteLine( );

int globalTotal = globalAllmanCount+globalKAndRCount+globalMixedCount;
Console.WriteLine( $"K&R style: \t{globalKAndRCount*100f/globalTotal:0.00}%" );
Console.WriteLine( $"Allman style: \t{globalAllmanCount*100f/globalTotal:0.00}%" );
Console.WriteLine( $"mixed style: \t{globalMixedCount*100f/globalTotal:0.00}%" );