README.md

1357. Apply Discount Every n Orders

There is a sale in a supermarket, there will be a discount every n customer. There are some products in the supermarket where the id of the i-th product is products[i] and the price per unit of this product is prices[i]. The system will count the number of customers and when the n-th customer arrive he/she will have a discount on the bill. (i.e if the cost is x the new cost is x - (discount * x) / 100). Then the system will start counting customers again. The customer orders a certain amount of each product where product[i] is the id of the i-th product the customer ordered and amount[i] is the number of units the customer ordered of that product.

Implement the Cashier class:

• Cashier(int n, int discount, int[] products, int[] prices) Initializes the object with n, the discount, the products and their prices.
• double getBill(int[] product, int[] amount) returns the value of the bill and apply the discount if needed. Answers within 10^-5 of the actual value will be accepted as correct.

Example 1:

Input:
["Cashier","getBill","getBill","getBill","getBill","getBill","getBill","getBill"]
[[3,50,[1,2,3,4,5,6,7],[100,200,300,400,300,200,100]],[[1,2],[1,2]],[[3,7],[10,10]],[[1,2,3,4,5,6,7],[1,1,1,1,1,1,1]],[[4],[10]],[[7,3],[10,10]],[[7,5,3,1,6,4,2],[10,10,10,9,9,9,7]],[[2,3,5],[5,3,2]]]
Output:
[null,500.0,4000.0,800.0,4000.0,4000.0,7350.0,2500.0]
Explanation:
Cashier cashier = new Cashier(3,50,[1,2,3,4,5,6,7],[100,200,300,400,300,200,100]);
cashier.getBill([1,2],[1,2]);                        // return 500.0, bill = 1 * 100 + 2 * 200 = 500.
cashier.getBill([3,7],[10,10]);                      // return 4000.0
cashier.getBill([1,2,3,4,5,6,7],[1,1,1,1,1,1,1]);    // return 800.0, The bill was 1600.0 but as this is the third customer, he has a discount of 50% which means his bill is only 1600 - 1600 * (50 / 100) = 800.
cashier.getBill([4],[10]);                           // return 4000.0
cashier.getBill([7,3],[10,10]);                      // return 4000.0
cashier.getBill([7,5,3,1,6,4,2],[10,10,10,9,9,9,7]); // return 7350.0, Bill was 14700.0 but as the system counted three more customers, he will have a 50% discount and the bill becomes 7350.0
cashier.getBill([2,3,5],[5,3,2]);                    // return 2500.0

Constraints:

• 1 <= n <= 10^4
• 0 <= discount <= 100
• 1 <= products.length <= 200
• 1 <= products[i] <= 200
• There are not repeated elements in the array products.
• prices.length == products.length
• 1 <= prices[i] <= 1000
• 1 <= product.length <= products.length
• product[i] exists in products.
• amount.length == product.length
• 1 <= amount[i] <= 1000
• At most 1000 calls will be made to getBill.
• Answers within 10^-5 of the actual value will be accepted as correct.

Solutions (Rust)

1. Solution

struct Cashier {
    n: i32,
    discount: f64,
    customers: i32,
    prices: Vec<i32>,
}


/** 
 * `&self` means the method takes an immutable reference.
 * If you need a mutable reference, change it to `&mut self` instead.
 */
impl Cashier {

    fn new(n: i32, discount: i32, products: Vec<i32>, prices: Vec<i32>) -> Self {
        let mut p = vec![0; 201];

        for i in 0..prices.len() {
            p[products[i] as usize] = prices[i];
        }

        Self {
            n: n,
            discount: discount as f64,
            customers: 0,
            prices: p,
        }
    }

    fn get_bill(&mut self, product: Vec<i32>, amount: Vec<i32>) -> f64 {
        let mut cost = 0;
        self.customers += 1;

        for i in 0..amount.len() {
            cost += self.prices[product[i] as usize] * amount[i];
        }

        match self.customers % self.n {
            0 => cost as f64 - (self.discount * cost as f64) / 100.0,
            _ => cost as f64,
        }
    }
}

/**
 * Your Cashier object will be instantiated and called as such:
 * let obj = Cashier::new(n, discount, products, prices);
 * let ret_1: f64 = obj.get_bill(product, amount);
 */