Remove /category/ and parent category slug

remove-category-and-parent-category.php

<?php
/*
* Author: Le Van Toan
* Link more update: http://levantoan.com/xoa-bo-category-va-slug-category-cha-khoi-duong-dan-category/
*/
// Remove Parent Category from Child Category URL
add_filter('term_link', 'devvn_no_category_parents', 1000, 3);
function devvn_no_category_parents($url, $term, $taxonomy) {
    if($taxonomy == 'category'){
        $term_nicename = $term->slug;
        $url = trailingslashit(get_option( 'home' )) . user_trailingslashit( $term_nicename, 'category' );
    }
    return $url;
}
// Rewrite url mới
function devvn_no_category_parents_rewrite_rules($flash = false) {
    $terms = get_terms( array(
        'taxonomy' => 'category',
        'post_type' => 'post',
        'hide_empty' => false,
    ));
    if($terms && !is_wp_error($terms)){
        foreach ($terms as $term){
            $term_slug = $term->slug;
            add_rewrite_rule($term_slug.'/?$', 'index.php?category_name='.$term_slug,'top');
            add_rewrite_rule($term_slug.'/page/([0-9]{1,})/?$', 'index.php?category_name='.$term_slug.'&paged=$matches[1]','top');
            add_rewrite_rule($term_slug.'/(?:feed/)?(feed|rdf|rss|rss2|atom)/?$', 'index.php?category_name='.$term_slug.'&feed=$matches[1]','top');
        }
    }
    if ($flash == true)
        flush_rewrite_rules(false);
}
add_action('init', 'devvn_no_category_parents_rewrite_rules');

/*Sửa lỗi khi tạo mới category bị 404*/
function devvn_new_category_edit_success() {
    devvn_no_category_parents_rewrite_rules(true);
}
add_action('created_category','devvn_new_category_edit_success');
add_action('edited_category','devvn_new_category_edit_success');
add_action('delete_category','devvn_new_category_edit_success');

This one doesnt seem to work for anything other than posts