/**
 * Given a list of customers and a list of products, this function returns a list
 * containing the common products that all customers have not purchased before.
 *
 * @param customers A list representing the customers.
 * @param products A list representing the available products.
 * @return A list containing the common products not purchased by any customer.
 */
fun findCommonProducts(customers: List<List<String>>, products: List<String>): List<String> {

    val commonProducts = mutableListOf<String>()
    
    if (customers.isEmpty()) {
        return commonProducts
    }
    
    for (product in products) {
        if (customers.all { customer -> product !in customer }) {
            commonProducts.add(product)
        }
    }
    
    return commonProducts
}
/**
 * Given a list of customers and a list of products, this function returns a list
 * containing the common products that all customers have not purchased before.
 *
 * @param customers A list representing the customers.
 * @param products A list representing the available products.
 * @return A list containing the common products not purchased by any customer.
 */
fun findCommonProducts(customers: List<List<String>>, products: List<String>): List<String> {
/**
 * Given a list of customers and a list of products, this function returns a list
 * containing the common products that all customers have not purchased before.
 *
 * @param customers A list representing the customers.
 * @param products A list representing the available products.
 * @return A list containing the common products not purchased by any customer.
 */
fun findCommonProducts(customers: List<List<String>>, products: List<String>): List<String> {

    val commonProducts = mutableListOf<String>()
    
    if (customers.isEmpty()) {
        return commonProducts
    }
    
    for (product in products) {
        if (customers.all { customer -> product !in customer }) {
            commonProducts.add(product)
        }
    }
    
    return commonProducts
}