Topic: Methods and Control Structures
Common Queries
- Defining methods
- Method parameters
- Conditional statements
- For/While loops
- Iteration
- Method Implementation
This question involves the AppointmentBook class, which provides methods for students to schedule appointments with their teacher. Appointments can be scheduled during one of eight class periods during the school day, numbered 1 through 8. A requested appointment has a duration, which is the number of minutes the appointment will last. The 60 minutes within a period are numbered 0 through 59. In order for an appointment to be scheduled, the teacher must have a block of consecutive, available munites that contains at least the requested number of minutes in a requested period. Scheduled appointments must start and end within the same period.
The AppointmentBook class contains two helper methods, isMinuteFree and reserveBlock. You will write two additional methods of the AppointmentBook class.
public class AppointmentBook {
/**
* Returns true if minute in period is available for an appointment and returns
* false otherwise
* Preconditions: 1 <= period <= 8; 0 <= minute <= 59
*/
private boolean isMinuteFree(int period, int minute) {
/* implementation not shown */
return false;
}
/**
* Marks the block of minutes that starts at startMinute in period and
* is duration minutes long as reserved for an appointment
* Preconditions: 1 <= period <= 8; 0 <= startMinute <= 59;
* 1 <= duration <= 60
*/
private void reserveBlock(int period, int startMinute, int duration) {
/* implementation not shown */
}
/**
* Searches for the first block of duration free minutes during period, as described in
* part (a). Returns the first minute in the block if such a block is found or returns -1 if no
* such block is found.
* Preconditions: 1 <= period <= 8; 1 <= duration <= 60
*/
public int findFreeBlock(int period, int duration) {
/* to be implemented in part (a) */
return 0;
}
/**
* Searches periods from startPeriod to endPeriod, inclusive, for a block
* of duration free minutes, as described in part (b). If such a block is found,
* calls reserveBlock to reserve the block of minutes and returns true; otherwise
* returns false.
* Preconditions: 1 <= startPeriod <= endPeriod <= 8; 1 <= duration <= 60
*/
public boolean makeAppointment(int startPeriod, int endPeriod, int duration) {
/* to be implemented in part (b) */
return false;
}
// There may be instance variables, constructors, and methods that are not shown.
}
Write the findFreeBlock method, which searches period for the first block of free minutes that is duration minutes long. If such a block is found, findFreeBlock returns the first minute in the block. Otherwise, findFreeBlock returns -1. The findFreeBlock method uses the helper method isMinuteFree, which returns true if a particular minute is available to be included in a new appointment and returns false if the minute is unavailable. The method call findFreeBlock(2, 15) would return 30 to indicate that a 15-minute block starting with minute 30 is available. No steps should be taken as a result of the call to findFreeBlock to mark those 15 minutes as unavailable. The method call findFreeBlock(2, 9) would also return 30. Whenever there are multiple blocks that satisfy the requirement, the earliest starting minute is returned. The method call findFreeBlock(2, 20) would return -1, since no 20-minute block of available minutes exists in period 2.
Complete method findFreeBlock. You must use isMinuteFree appropriately in order to receive full credit.
/**
* Searches for the first block of duration free minutes during the specified period.
* Returns the first minute in the block if such a block is found or returns -1 if no such block is found.
*
* @param period The period to search for free minutes.
* @param duration The duration of the free block to find.
* @return The first minute in the found free block or -1 if no such block is found.
*
* Preconditions: 1 <= period <= 8; 1 <= duration <= 60
*/
public int findFreeBlock(int period, int duration) {
// Implementation of finding and returning the first minute of a free block.
// This is where you would add your code to perform the search.
return 0;
}
My Answer:
public int findFreeBlock(int period, int duration) {
// Loop through the minutes in the specified period
for (int startMinute = 0; startMinute <= 59 - duration; startMinute++) {
boolean isBlockFree = true;
// Check if the block of minutes from startMinute to (startMinute + duration - 1) is free
for (int minute = startMinute; minute < startMinute + duration; minute++) {
if (!isMinuteFree(period, minute)) {
isBlockFree = false;
break; // Exit the inner loop if any minute in the block is not free
}
}
// If a free block of the requested duration is found, return the start minute
if (isBlockFree) {
return startMinute;
}
}
// If no free block of the requested duration is found, return -1
return -1;
}
To test my code:
public class AppointmentBookTester {
public static void main(String[] args) {
// Create an instance of the AppointmentBook class
AppointmentBook appointmentBook = new AppointmentBook();
// Test the findFreeBlock method
int period = 2;
int duration1 = 15;
int duration2 = 9;
int duration3 = 20;
int freeBlock1 = appointmentBook.findFreeBlock(period, duration1);
int freeBlock2 = appointmentBook.findFreeBlock(period, duration2);
int freeBlock3 = appointmentBook.findFreeBlock(period, duration3);
System.out.println("Testing findFreeBlock:");
System.out.println("Duration 15 minutes, start minute: " + freeBlock1);
System.out.println("Duration 9 minutes, start minute: " + freeBlock2);
System.out.println("Duration 20 minutes, start minute: " + freeBlock3);
// Test the makeAppointment method
int startPeriod = 3;
int endPeriod = 6;
int appointmentDuration = 30;
boolean appointment1 = appointmentBook.makeAppointment(startPeriod, endPeriod, appointmentDuration);
boolean appointment2 = appointmentBook.makeAppointment(5, 7, 45);
System.out.println("\nTesting makeAppointment:");
System.out.println("Appointment 1 (start period 3, end period 6, duration 30): " + appointment1);
System.out.println("Appointment 2 (start period 5, end period 7, duration 45): " + appointment2);
}
}
AppointmentBookTester.main(null);
Testing findFreeBlock:
Duration 15 minutes, start minute: 0
Duration 9 minutes, start minute: 0
Duration 20 minutes, start minute: 0
Testing makeAppointment:
Appointment 1 (start period 3, end period 6, duration 30): false
Appointment 2 (start period 5, end period 7, duration 45): false
The Actual Solution:
public int findFreeBlock(int period, int duration)
{
int freeInARow = 0;
for(int minute = 0; minute <= 59; minute++)
{
if(isMinuteFree(period, minute))
freeInARow++;
else
freeInARow = 0;
if(freeInARow == duration)
return minute - freeInARow + 1;
}
return -1;
}
public boolean makeAppointment(int startPeriod, int endPeriod,
int duration)
{
for(int period = startPeriod; period <= endPeriod; period++)
{
int startMinute = findFreeBlock(period, duration);
if(startMinute != -1)
{
reserveBlock(period, startMinute, duration);
return true;
}
}
return false;
}
Regarding Array/ArrayList/2D Arrays
- Change or add data to arrays, easier for ArrayList. How would you do it for others?
- Displaying Array/ArrayList by columns, as well as by rows horizontally
- Display content backwards
import java.util.ArrayList;
import java.util.Arrays;
import java.util.Collections;
import java.util.List;
public class ArrayManipulation {
public static void main(String[] args) {
// Arrays
int[] intArray = {1, 2, 3, 4, 5};
String[] stringArray = {"apple", "banana", "cherry", "date", "fig"};
// ArrayLists
List<Integer> intArrayList = new ArrayList<>(Arrays.asList(1, 2, 3, 4, 5));
List<String> stringArrayList = new ArrayList<>(Arrays.asList("apple", "banana", "cherry", "date", "fig"));
// Changing values in arrays
intArray[2] = 30;
stringArray[4] = "grape";
// Adding data to ArrayLists
intArrayList.add(6);
stringArrayList.add("honeydew");
// Displaying Arrays/ArrayLists by columns
System.out.println("Displaying Arrays by columns:");
for (int i = 0; i < intArray.length; i++) {
System.out.println(intArray[i] + "\t" + stringArray[i]);
}
System.out.println("\nDisplaying ArrayLists by columns:");
for (int i = 0; i < intArrayList.size(); i++) {
System.out.println(intArrayList.get(i) + "\t" + stringArrayList.get(i));
}
// Displaying Arrays/ArrayLists horizontally
System.out.println("\nDisplaying Arrays horizontally:");
System.out.println(Arrays.toString(intArray));
System.out.println(Arrays.toString(stringArray));
System.out.println("\nDisplaying ArrayLists horizontally:");
System.out.println(intArrayList);
System.out.println(stringArrayList);
// Displaying content backwards
System.out.println("\nDisplaying Arrays backwards:");
for (int i = intArray.length - 1; i >= 0; i--) {
System.out.print(intArray[i] + " ");
}
System.out.println();
for (int i = stringArray.length - 1; i >= 0; i--) {
System.out.print(stringArray[i] + " ");
}
System.out.println("\nDisplaying ArrayLists backwards:");
Collections.reverse(intArrayList);
Collections.reverse(stringArrayList);
System.out.println(intArrayList);
System.out.println(stringArrayList);
}
}
ArrayManipulation.main(null);
Displaying Arrays by columns:
1 apple
2 banana
30 cherry
4 date
5 grape
Displaying ArrayLists by columns:
1 apple
2 banana
3 cherry
4 date
5 fig
6 honeydew
Displaying Arrays horizontally:
[1, 2, 30, 4, 5]
[apple, banana, cherry, date, grape]
Displaying ArrayLists horizontally:
[1, 2, 3, 4, 5, 6]
[apple, banana, cherry, date, fig, honeydew]
Displaying Arrays backwards:
5 4 30 2 1
grape date cherry banana apple
Displaying ArrayLists backwards:
[6, 5, 4, 3, 2, 1]
[honeydew, fig, date, cherry, banana, apple]
Feedback on My FRQ
Feedback on Rohin’s FRQ.
From the crossover team, Rohin did the same type of FRQ as me, Methods & Control Structures. Here is his code:
public int getScore() {
int multiplier = isBonus() ? 3 : 1;
if (levelOne.goalReached() && levelTwo.goalReached()) {
if (levelThree.goalReached())
return (levelOne.getPoints()+levelTwo.getPoints()+levelThree.getPoints())*multiplier;
else
return (levelOne.getPoints()+levelTwo.getPoints())*multiplier;
} else {
return levelOne.getPoints()*multiplier;
}
}
public int playManyTimes(int num, boolean[] isBonuses) {
ArrayList<Integer> scores = new ArrayList<Integer>();
for (int i = 0; i < num; i++) {
this.play(isBonuses[i]);
scores.add(this.getScore());
System.out.println(scores.get(i));
}
int largestScore = scores.get(0);
for (int i = 0; i < scores.size(); i++) {
if (scores.get(i) > largestScore) largestScore = scores.get(i);
}
return largestScore;
}
And here is the canonical code from CollegeBoard:
public int getScore()
{
int score = 0;
if (levelOne.goalReached())
{
score = levelOne.getPoints();
if (levelTwo.goalReached())
{
score += levelTwo.getPoints();
if (levelThree.goalReached())
{
score += levelThree.getPoints();
}
}
}
if (isBonus())
{
score *= 3;
}
return score;
}
4 points
(b) public int playManyTimes(int num)
{
int max = 0;
for (int i = 0; i < num; i++)
{
play();
int score = getScore();
if (score > max)
{
max = score;
}
}
return max;
}
The first thing Rohin could’ve improved on was the getScore() method. Instead of using the concept of a multi-conditional statement, he could’ve used the concept of nested conditionals to make the code more efficient. Another thing he could’ve done different is in the playManyTimes() method, where he could’ve avoided the use of ArrayLists altogether and instead used one loop as shown in the CollegeBoard code. Other than that, the code is great, and I have no additional feedback. I like how the concepts of methods and control structures as well as the common queries are represented in the overall code and the presentation.