leetcode1357

class Cashier:
    def __init__(self, n: int, discount: int, products: 'List[int]', prices: 'List[int]'):
        self.customer_num = 0
        self.dic = {}
        m = len(products)
        for i in range(m):
            self.dic[products[i]] = prices[i]
        self.n = n
        self.discount = discount


    def getBill(self, product: 'List[int]', amount: 'List[int]') -> float:
        self.customer_num += 1
        self.customer_num %= self.n
        m = len(product)
        total_amount = 0
        for i in range(m):
            productid = product[i]
            amt = amount[i]
            total_amount += (self.dic[productid] * amt)
        if self.customer_num == 0:
            total_amount = total_amount - (self.discount * total_amount) / 100
        return total_amount

算法思路：将products[]与prices[]建立映射字典，这样可以方便查询每一种商品对应的单价。

每增加一个用户，累加一次用户数量，并用n进行求模运算，每第n个用户就计算折扣。