Nested Wordpress Menu excluding duplicate posts.

<?php
$url = explode('/', $_SERVER['REQUEST_URI']);
$dir = $url[2] ? $url[2] : 'UX-Style-Guide';
$result = str_replace ("?","",$dir);
$final = current(explode('=', $result));
$style = str_replace ("-"," ",$final);
$style = ucwords($style);
$post_id = $post->ID;
$class = '';

function displayPosts($categoryObj, &$displayedPosts, $post_id, $final) {
  $nav_post_args = array(
    'numberposts' => -1,
    'category' => $categoryObj->term_id,
    'post_type' => $final,
    'orderby' => 'name',
    'order' => 'ASC',
    'child_of' => 0
  );

  $nav_posts = get_posts($nav_post_args);
  $output = '';

  foreach($nav_posts as $post) {
    if (in_array($post->ID, $displayedPosts)) {
      continue; //Skip this post if it has already been displayed once.
    }

    $title = the_title();
    $link = the_permalink();

    if ($title === '→') {
      continue; //Help avoid output weirdness
    }

    $displayedPosts[] = $post->ID;
    $class = '';

    if ($post_id == $post->ID) {
      $class = 'entry-title current';
    } else {
      $class = 'entry-title';
    }

    $output .= "<li class='$class'>";
    $output .= "<a class='entry-link' href='$link'>$title</a>";
    $output .= "</li>\n";
  }

  return $output;
}
?>

<!-- THIS IS THE LEFTNAV -->
<nav id="verticalNav" class="ui-side-nav-drawer">
  <div class="cssmenu">
    <div id="entry-search">
      <input type="text" placeholder="Search Styleguide Entries" class="fuzzy-search" />
    </div>
    <ul class="list">
      <?php
        $nav_cat_args = array(
          'orderby' => 'name',
          'order' => 'ASC',
          'child_of' => 0,
          'exclude'=> 1
        );

        $nav_categories = get_categories($nav_cat_args);
        $displayedPosts = array();

        foreach($nav_categories as $category) {
          echo "<li><span class='navAppTitle'>" . $category->name . "</span></li>\n";
          echo displayPosts($category, $displayedPosts, $post_id, $final);

          $subcatArgs = array('parent' => $category->ID);
          $subCategories = get_categories($subcatArgs);

          foreach ($subCategories as $subCategory) {
            echo "<ul class='subCategoryList'>\n";
            echo "<li><span class='navAppTitle subCategory'>" . $subCategory->name . "</span></li>\n";
            echo displayPosts($subCategory, $displayedPosts, $post_id, $final);
            echo "</ul>\n";
          }
        }
      ?>

      <?php wp_reset_query(); ?>

      <div id="job-listings"></div>
    </ul>
  </div>

</nav><!-- /END #verticalNav -->