pre:

set-strictmode -version 2.0


$folders = Get-ChildItem C:\Windows\System32\catroot -Force -Recurse | Where-Object{($_.PSIsContainer)} | Select Name, FullName

$filesize_list = @()

ForEach($folder in $folders){
     $name = [Guid]::Empty
     if([Guid]::TryParse($folder.Name,[ref]$name))
     {
        $filesize_list += Get-Item $folder.FullName | Select -Property FullName,@{Name="Size"; `
                          Expression = {(Get-ChildItem $_.FullName | Measure-Object -property length -sum).Sum + 0}}
     }
}

$file_groups = $filesize_list | Select FullName, Size | Group-Object -Property Size | Where-Object {($_.Count -gt 1) -and ($_.Name -gt 0)} `
               | Select Name, @{Name="Group"; Expression = {$_.Group.FullName}} 

$file_hashes = @{}

ForEach( $file_group in $file_groups){
    ForEach( $file_to_hash in $file_group.Group){
        $file_hashes.Add( $file_to_hash, (Get-ChildItem $file_to_hash -Force -Recurse | Get-FileHash | Select Hash))
    }
}
$file_hashes.GetEnumerator() | Group-Object -Property Value | Select Count, @{Name="Matches"; Expression = {$_.Group.Name}} `
                | Out-GridView -OutputMode Single | Select -ExpandProperty Group