FRQ 1 - 2019

This frq from 2019 deals with a calendar where you have to write two methods of the class in order to calculate the number of leap years between year1 and year2 inclusively as well as write a method that returns an integer representing the day of the week for the given date (month, day, year).

Part A

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.

// Part A solution

public static int numberOfLeapYears(int year1, int year2){
    int numLeapYears = 0;
    for(int i = year1; i <= year2, i++){
        if(isLeapYear(i)){
            numLeapYears++;
        }
    }
    return numLeapYears;
}

Part B

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. As another example, January 10 is the tenth day of 2019. As a result, January 10, 2019, fell on a Thursday, and the method call dayOfWeek(1, 10, 2019) returns 4. In order to calculate this value, two helper methods are provided for you. • firstDayOfYear(year) returns the integer value representing the day of the week for the first day of year, where 0 denotes Sunday, 1 denotes Monday, ..., and 6 denotes Saturday. For example, since 2019 began on a Tuesday, firstDayOfYear(2019) returns 2. • dayOfYear(month, day, year) returns n, where month, day, and year specify the nth day of the year. For the first day of the year, January 1 (month = 1, day = 1), the value 1 is returned. This method accounts for whether year is a leap year. For example, dayOfYear(3, 1, 2017) returns 60, since 2017 is not a leap year, while dayOfYear(3, 1, 2016) returns 61, since 2016 is a leap year. Complete method dayOfWeek below. You must use firstDayOfYear and dayOfYear appropriately to receive full credit.

// Part B Solution
public static int daysOfWeek(int month, int day, int year){
    int firstDay = firstDayOfYear(year);
    int nth = dayOfYear(month, day, year);
    int returnDay = ((firstDay + nth) -1) % 7;
    return returnDay;
}

Completed Code

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){
        int numLeapYears = 0;
        for(int i = year1; i <= year2, i++){
            if(isLeapYear(i)){
                numLeapYears++;
            }
        }
        return numLeapYears;
    }
    /** 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 daysOfWeek(int month, int day, int year){
        int firstDay = firstDayOfYear(year);
        int nth = dayOfYear(month, day, year);
        int returnDay = ((firstDay + nth) -1) % 7;
        return returnDay;
    }
    // There may be instance variables, constructors, and other methods not shown.
}