WORDPRESS Track post views without a plugin using post meta

<?php
// Add this to functions.php
function getPostViews($postID){
    $count_key = 'post_views_count';
    $count = get_post_meta($postID, $count_key, true);
    if($count==''){
        delete_post_meta($postID, $count_key);
        add_post_meta($postID, $count_key, '0');
        return "0 View";
    }
    return $count.' Views';
}
function setPostViews($postID) {
    $count_key = 'post_views_count';
    $count = get_post_meta($postID, $count_key, true);
    if($count==''){
        $count = 0;
        delete_post_meta($postID, $count_key);
        add_post_meta($postID, $count_key, '0');
    }else{
        $count++;
        update_post_meta($postID, $count_key, $count);
    }
}

// Place this snippet bellow “setPostViews” within the single.php inside the loop
<?php setPostViews(get_the_ID()); ?>

// Add this to your template
<?php
query_posts('meta_key=post_views_count&orderby=meta_value_num&order=DESC');
?>

Source:
http://wpsnipp.com/index.php/functions-php/track-post-views-without-a-plugin-using-post-meta/
http://wpsnipp.com/index.php/loop/most-popular-posts-using-views-post-meta/