Fatal error: Class 'Diffbot' not found

[lesterjanpearson]

require_once("../diffbot-php-client/vendor/autoload.php");

$diffbot = new Diffbot($token);
$url = 'http://www.sitepoint.com/diffbot-crawling-visual-machine-learning/';
$articleApi = $diffbot->createArticleAPI($url);

[ericsala]

Probably you are not using the correct namespace.
Try with...
$diffbot = new Swader\Diffbot\Diffbot($token);
$url = 'http://www.sitepoint.com/diffbot-crawling-visual-machine-learning/';
$articleApi = $diffbot->createArticleAPI($url);