AP CSA FRQ Practice

• AP CSA 2019 FRQ

AP CSA 2019 FRQ

The APCalendar class contains methods used to calculate information about a calendar. You will write two methods of the class.

public class APCalendar
{
 /** Returns true if year is a leap year and false otherwise. */
    private static boolean isLeapYear(int year)
 { /* implementation not shown */ }
 /** Returns the number of leap years between year1 and year2, inclusive.
 * Precondition: 0 <= year1 <= year2
 */
    public static int numberOfLeapYears(int year1, int year2)
 { /* to be implemented in part (a) */ }
 /** Returns the value representing the day of the week for the first day of year,
 * where 0 denotes Sunday, 1 denotes Monday, ..., and 6 denotes Saturday.
 */
     private static int firstDayOfYear(int year)
 { /* implementation not shown */ }
 /** Returns n, where month, day, and year specify the nth day of the year.
 * Returns 1 for January 1 (month = 1, day = 1) of any year.
 * Precondition: The date represented by month, day, year is a valid date.
 */
     private static int dayOfYear(int month, int day, int year)
 { /* implementation not shown */ }
 /** Returns the value representing the day of the week for the given date
 * (month, day, year), where 0 denotes Sunday, 1 denotes Monday, ...,
 * and 6 denotes Saturday.
 * Precondition: The date represented by month, day, year is a valid date.
 */
    public static int dayOfWeek(int month, int day, int year)
 { /* to be implemented in part (b) */ }
 // There may be instance variables, constructors, and other methods not shown.
}

Write the static method numberOfLeapYears, which returns the number of leap years between year1 and year2, inclusive.

In order to calculate this value, a helper method is provided for you. • isLeapYear(year) returns true if year is a leap year and false otherwise.

Complete method numberOfLeapYears below. You must use isLeapYear appropriately to receive full credit.

/** Returns the number of leap years between year1 and year2, inclusive.

• Precondition: 0 <= year1 <= year2 */

  public static int numberOfLeapYears(int year1, int year2)

public static int numberOfLeapYears(int year1, int year2){
    int numyear = 0;
        if(isLeapYear(int year)){ 
            numyear ++;
        }
    }
    return numyear;

I was a bit confused about how to go through each year and how to reference this when checking whether each year is a leap year.

Correct Answer:

//keep track of number of leap years
//loop through year 1 to year 2
public static int numberOfLeapYears(int year1, int year2)
{
    int count = 0;
    for (int y = year1; y <= year2; y++) //loop through the years as long as they are less than or equal to year 2 -> keep adding to years
    {
        if (isLeapYear(y)) //if the year is a leap year
    {
        count++; //increase count variable by 1
    }
    }
    return count; //return count (the number of times a leap year was found)
}

Score: 3/5

• Initialize numeric variable (numyear)
• Loop through each necessary year in range
• Calls isLeapYear on valid year in range
• Update count based on result of isLeapYear
• Return count of leap years

Write the static method dayOfWeek, which returns the integer value representing the day of the week for the given date (month, day, year), where 0 denotes Sunday, 1 denotes Monday, ..., and 6 denotes Saturday. For example, 2019 began on a Tuesday, and January 5 is the fifth day of 2019. As a result, January 5, 2019, fell on a Saturday, and the method call dayOfWeek(1, 5, 2019) returns 6.

public static int dayOfWeek(int year, int day)
{
 int countday1 = firstDayOfYear(year);
 int countDay = dayOfYear(month, day);
 int  = (countday1 + countDay) % 7;
}

Answer:

public static int dayOfWeek(int month, int day, int year)
{
 int startDay = firstDayOfYear(year); //find first day of year
 int nthDay = dayOfYear(month, day, year); //find day of year
 int returnDay = (startDay + nthDay - 1) % 7; // the start and last day get added and -1 (because of Sunday) and /7 in order to find which day of the week it is 
 return returnDay; //the returned number will tell us how many days away it is from the start day
}

Score: 3/5

Need to add integer for month number Need to return value Wrong calculations