Google+ Post about it: https://plus.google.com/104695723888883478740/posts/MfBnVkqbeHH | Online version: http://folyam.info/google-play-activity.php

google-play-activity.php

<?php
if (array_key_exists('profileUrl', $_POST)) {
  $url = $_POST['profileUrl'];
} else {
  $url = "https://plus.google.com/u/0/+SergeyBrin/posts";
}

$url = preg_replace('/u\/\d+\//', '', $url);

$ch = curl_init();
curl_setopt($ch, CURLOPT_URL, $url);
curl_setopt($ch, CURLOPT_RETURNTRANSFER, true);
curl_setopt($ch, CURLOPT_SSL_VERIFYPEER, false);
$response = curl_exec($ch);

preg_match('/data:\["(\d+)",/', $response, $matches);
$profileId = $matches[1];

preg_match('/<title itemprop="name">(.*) - Google\+<\/title>/', $response, $matches);
$name = $matches[1];

echo "<h1>Google Play Activity: " . htmlentities($name) . "</h1>";

$url = 'https://play.google.com/store/people/details?id=' . $profileId;

echo "<a href='" . $url . "' target='_blank'>" . $url . "</a>";
?>

<form method="post">
  Profile URL: <input type="text" name="profileUrl" placeholder="Google+ Profile URL">
  <input type="submit" value="Get the Activity URL">
</form>

<h2>Examples:</h2>
<ul>
  <li>https://plus.google.com/u/0/+SergeyBrin/posts</li>
  <li>https://plus.google.com/u/0/+YehudaKatz/posts</li>
</ul>