bejes

function get_deep_child_category()
{
$categories = get_the_category();
    $maxId = 0;
    $maxKey = 0;
    foreach ( $categories as $key => $value )
    {
        if ( $value->parent > $maxId )
        {
            $maxId = $value->term_id;

bejes

<?php 

if (is_single() || is_category()) {
$category = get_the_category();
$nice_name=array();
foreach($category as $c)
{
  $parent = $c->category_parent;
  $parent_cat =get_category($parent);
  $nice_name[]= $parent_cat->category_nicename;