wordpress: Get last child category ID

gistfile1.php

<?php 
//Get all terms associated with post in taxonomy 'category'
$terms = get_the_terms(get_the_ID(),'category');

//Get an array of their IDs
$term_ids = wp_list_pluck($terms,'term_id');

//Get array of parents - 0 is not a parent
$parents = array_filter(wp_list_pluck($terms,'parent'));

//Get array of IDs of terms which are not parents.
$term_ids_not_parents = array_diff($term_ids,  $parents);

//Get corresponding term objects
$terms_not_parents = array_intersect_key($terms,  $term_ids_not_parents);
//print_r($terms_not_parents);
echo key($terms_not_parents);