while(<>)
{
    chomp;
    $s = length $_;
    @bs = split //;
    $bucket{$_}++ foreach(@bs);
    
    while(keys %bucket)
    {
        $tuple = "";
        %old_b = { %bucket };
        foreach(sort keys(%bucket))
        {
            last if( length $tuple == 4);
            if($bucket{$_} >= 4 && length $tuple==0)
            {
                $tuple = $_ x 4;
                $bucket{$_}-=4;
                last;
            }
            else
            {
                if($bucket{$_} > 0)
                {
                    $tuple .= $_;
                    $bucket{$_}--;
                }
                else { last; }
            }
        }
        if(length $tuple == 4){ print "$tuple\n"; }
        else { %bucket = %old_b; }
        
        foreach( keys(%bucket)){ (delete $bucket{$_}) if ($bucket{$_} 
+== 0); }
    }
}
[download]