The challenge

After a hard quarter in the office you decide to get some rest on a vacation. So you will book a flight for you and your girlfriend and try to leave all the mess behind you.

You will need a rental car in order for you to get around in your vacation. The manager of the car rental makes you some good offers.

Every day you rent the car costs $40. If you rent the car for 7 or more days, you get $50 off your total. Alternatively, if you rent the car for 3 or more days, you get $20 off your total.

Write a code that gives out the total amount for different days(d).

The solution in Java code

Option 1:

public class Solution {
  public static int rentalCarCost(int d) {
    int totalBefore = d * 40;
    if (d>=7) return totalBefore-50;
    if (d>=3) return totalBefore-20;
    return totalBefore;
  }
}

Option 2:

public class Solution {
  private static final int COST_PER_DAY = 40;
  public static int rentalCarCost(int d) {
    if (d < 3)       return d * COST_PER_DAY;
    else if (d >= 7) return d * COST_PER_DAY - 50;
    else             return d * COST_PER_DAY - 20;
  }
}

Option 3:

public class Solution {
  public static int rentalCarCost(int d) {
    return d < 7 ? d < 3 ? 40 * d : 40 * d - 20 : 40 * d - 50;
  }
}

Test cases to validate our solution

import org.junit.Test;
import static org.junit.Assert.assertEquals;
public class RentalCarExampleTests {
  @Test
  public void under3Tests() {
    assertEquals(40, Solution.rentalCarCost(1));
    assertEquals(80, Solution.rentalCarCost(2));
  }
  @Test
  public void under7Tests() {
    assertEquals(100, Solution.rentalCarCost(3));
    assertEquals(140, Solution.rentalCarCost(4));
    assertEquals(180, Solution.rentalCarCost(5));
    assertEquals(220, Solution.rentalCarCost(6));
  }
  @Test
  public void over7Tests() {
    assertEquals(230, Solution.rentalCarCost(7));
    assertEquals(270, Solution.rentalCarCost(8));
    assertEquals(310, Solution.rentalCarCost(9));
    assertEquals(350, Solution.rentalCarCost(10));
  }
}