Auto Redirect to Post on Single Search Result

This snippet causes a redirect to the post when a WordPress search returns only one result, instead of displaying the search results page as usual.

function single_result() {
    if (is_search()) {
        global $wp_query;
        if ($wp_query->post_count == 1) {
            wp_redirect( get_permalink( $wp_query->posts['0']->ID ) );
        }
    }
}

add_action('template_redirect', 'single_result');

For more on WordPress search optimization, see Prevent Search Engines from Indexing Search Results.