每隔 n 个顾客打折

/* 思路：
   1. 使用 Java Stream API 优化代码。
   2. 使用 IntStream 和 mapToDouble 方法简化账单计算。
*/
import java.util.HashMap;
import java.util.Map;
import java.util.stream.IntStream;

public class Cashier {
    private int n;
    private int discount;
    private int customerCount;
    private Map<Integer, Integer> productPriceMap;

    public Cashier(int n, int discount, int[] products, int[] prices) {
        this.n = n;
        this.discount = discount;
        this.customerCount = 0;
        productPriceMap = new HashMap<>();
        for (int i = 0; i < products.length; i++) {
            productPriceMap.put(products[i], prices[i]);
        }
    }

    public double getBill(int[] product, int[] amount) {
        customerCount++;
        double total = IntStream.range(0, product.length)
                         .mapToDouble(i -> productPriceMap.get(product[i]) * amount[i])
                         .sum();
        if (customerCount % n == 0) {
            total -= (discount * total / 100.0);
        }
        return total;
    }
}