Design and code up a simple rating system that allows users to let others know whether a coupon is still valid. Keep in mind:

1) RetailMeNot has a massive user base, so efficiency is an important consideration.

2) We never want to mislead users. Given such a large user base, there are malicious users and you'll need to protect your rating system against scripts or ‘bots’.

3) Coupons are considered 'valid' when users receive the described discount after applying the coupon code to their purchase.

You may assume certain data structures, such as Coupons, Merchants, and Users, have been defined for you. You may also assume that you have access to fictitious APIs to retrieve such data, e.g., from a database. You should then write your code against such APIs. You may freely extend these data structures as desired, but please be sure to explain your design decisions.

Winning solutions will:

- Compile in the language of the contestant's choice

- Use the sample versions of the data structures we specified, or extends them as necessary

- Document any high-level algorithms and/or design decisions (including any extensions to the given data structures)

- Run with test input of the contestant's choice

Example definitions of Coupons, Merchants, and Users:

public class Coupon {

public String description;

public Date startDate;

public Date endDate;

public Merchant merchant;

public User submitter;

public int rating;

}

public class Merchant {

public String name;

}

public class User {

public String name;

}