Computer Science 9618/42 October/November 2025: question paper and mark scheme

Mark scheme

1(a)(i) 1 mark each 4 • Class header (and end) • 4 private attributes with correct data types • Constructor header (and end) taking 2 parameters within class … • … within constructor assigning parameters to Species and DistancePerHour and assigning 500.0 to XPosition and YPosition Example program code Java class Bird{ private String Species; private Double DistancePerHour; private Double XPosition; private Double YPosition; public Bird(Double pDistancePerHour, String pSpecies){ Species = pSpecies; DistancePerHour = pDistancePerHour; XPosition = 500.0; YPosition = 500.0;}} VB.NET Class Bird Private Species As String Private DistancePerHour As Single Private XPosition As Single Private YPosition As Single Sub New(pDistancePerHour, pSpecies) Species = pSpecies DistancePerHour = pDistancePerHour XPosition = 500.0 YPosition = 500.0 End Sub End Class 1(a)(i) Python class Bird: def __init__(self, pDistancePerHour, pSpecies): self.__Species = pSpecies #string self.__DistancePerHour = pDistancePerHour #real self.__XPosition = 500.0 #real self.__YPosition = 500.0 #real 1(a)(ii) 1 mark each 2 • Get method header (and end) with no parameter …. • … returning Species Example program code Java public String GetSpecies(){ return Species; } VB.NET Function GetSpecies() Return Species End Function Python def GetSpecies(self): return self.__Species 1(a)(iii) 1 mark each 3 • Get method header (and end) with no parameter, returning a value • Creating correct string using attributes … • … returning this string Example program code Java public String GetPosition(){ String ReturnValue = "X = " + XPosition + " Y = " + YPosition; return ReturnValue; } VB.NET Function GetPosition() Dim ReturnValue As String = "X = " & XPosition & " Y = " & YPosition Return ReturnValue End Function Python def GetPosition(self): ReturnValue = "X = " + str(self.__XPosition) + " Y = " + str(self.__YPosition) return ReturnValue 1(a)(iv) 1 mark each 5 • Method header (and end) taking direction and minutes flying as parameters • Calculation of distance using minutes flying parameter and attribute DistancePerHour • Selection based on direction parameter … • … north adding to YPosition and south subtracting from YPosition • … east adding to XPosition and west subtracting from XPosition Example program code Java public Boolean Move(String Direction, Integer MinsFlying){ if(Direction.compareTo("E") == 0){ XPosition = XPosition + ((DistancePerHour / 60) * MinsFlying); }else if(Direction.compareTo("W") == 0){ XPosition = XPosition - ((DistancePerHour / 60) * MinsFlying); }else if(Direction.compareTo("N") == 0){ YPosition = YPosition + ((DistancePerHour / 60) * MinsFlying); }else if(Direction.compareTo("S") == 0){ YPosition = YPosition - ((DistancePerHour / 60) * MinsFlying); } } 1(a)(iv) VB.NET Function Move(Direction, MinsFlying) If Direction = "E" Then XPosition = XPosition + ((DistancePerHour / 60) * MinsFlying) ElseIf Direction = "W" Then XPosition = XPosition - ((DistancePerHour / 60) * MinsFlying) ElseIf Direction = "N" Then YPosition = YPosition + ((DistancePerHour / 60) * MinsFlying) ElseIf Direction = "S" Then YPosition = YPosition - ((DistancePerHour / 60) * MinsFlying) End If End Function Python def Move(self, Direction, MinsFlying): if Direction == "E": self.__XPosition = self.__XPosition + ((self.__DistancePerHour/60)*MinsFlying) elif Direction == "W": self.__XPosition = self.__XPosition - ((self.__DistancePerHour/60)*MinsFlying) elif Direction == "N": self.__YPosition = self.__YPosition + ((self.__DistancePerHour/60)*MinsFlying) elif Direction == "S": self.__YPosition = self.__YPosition - ((self.__DistancePerHour/60)*MinsFlying) 1(b) 1 mark each 3 • Cockatiel 71.0 instance of Bird created … • Macaw 56.0 instance of Bird created … • … both stored in variables/structures Example program code Java Bird FirstBird = new Bird(71.0, "Cockatiel"); Bird SecondBird = new Bird(56.0, "Macaw"); VB.NET Dim FirstBird As Bird = New Bird(71.0, "Cockatiel") Dim SecondBird As Bird = New Bird(56.0, "Macaw") Python FirstBird = Bird(71.0, "Cockatiel") SecondBird = Bird(56.0, "Macaw") 1(c)(i) 1 mark each 8 • Output species, X and Y position for both Bird objects in appropriate messages(s) • Prompt and input of bird choice, time and direction … • … validating all three inputs … • … looping until all three are valid • Calling Move() for chosen bird … • … with only input direction and input time as arguments • Outputting new position for the bird moved • Using get methods throughout where appropriate Example program code Java Integer Choice; Integer Time; String Direction; Scanner scanner = new Scanner(System.in); Choice = 0; while(Choice != 1 && Choice != 2){ System.out.println("Which bird do you want to move"); System.out.println("Enter 1 for " + FirstBird.GetSpecies() + " is currently at " + FirstBird.GetPosition()); System.out.println("Enter 2 for " + SecondBird.GetSpecies() + " is currently at " + SecondBird.GetPosition()); Choice = Integer.parseInt(scanner.nextLine()); } Time = -1; while(Time < 0 or Time > 500){ System.out.println("To the nearest minute how long as the bird been flying?"); Time = Integer.parseInt(scanner.nextLine()); } Boolean Valid = false; while(Valid == false){ 1(c)(i) Valid = true; System.out.println("Which direction has the bird been flying, North, South, East or West?"); Direction = scanner.nextLine().toUpperCase(); if(Direction.compareTo("NORTH") == 0 || Direction.compareTo("N") == 0){ if(Choice == 1){ FirstBird.Move("N",Time); }else{ SecondBird.Move("N", Time); } } else if(Direction.compareTo("SOUTH")== 0 || Direction.compareTo("S") == 0){ if(Choice == 1){ FirstBird.Move("S",Time); }else{ SecondBird.Move("S", Time); } } else if(Direction.compareTo("EAST")== 0 || Direction.compareTo("E") == 0){ if(Choice == 1){ FirstBird.Move("E",Time); }else{ SecondBird.Move("E", Time); } } else if(Direction.compareTo("WEST")== 0 || Direction.compareTo("W") == 0){ if(Choice == 1){ FirstBird.Move("W",Time); }else{ SecondBird.Move("W", Time); } }else{ Valid = false; } } System.out.println(FirstBird.GetSpecies() + " is currently at " + FirstBird.GetPosition()); 1(c)(i) System.out.println(SecondBird.GetSpecies() + " is currently at " + SecondBird.GetPosition()); VB.NET Dim Choice As Integer Dim Time As Integer Dim Direction As String Choice = 0 While Choice <> 1 And Choice <> 2 Console.WriteLine("Which bird do you want to move") Console.WriteLine("Enter 1 for " & FirstBird.GetSpecies() & " is currently at " & FirstBird.GetPosition()) Console.WriteLine("Enter 2 for " & SecondBird.GetSpecies() & " is currently at " & SecondBird.GetPosition()) Choice = Console.ReadLine End While Time = -1 While Time < 0 Or Time > 500 Console.WriteLine("To the nearest minute how long has the bird been flying ") Time = Console.ReadLine End While Dim Valid As Boolean = False While (Valid = False) Valid = True Console.WriteLine("Which direction has the bird been flying, North, South, East or West ") Direction = Console.ReadLine().ToUpper If Direction = "NORTH" Or Direction = "N" Then If Choice = 1 Then FirstBird.Move("N", Time) Else SecondBird.Move("N", Time) End If 1(c)(i) ElseIf Direction = "SOUTH" Or Direction = "S" Then If Choice = 1 Then FirstBird.Move("S", Time) Else SecondBird.Move("S", Time) End If ElseIf Direction = "EAST" Or Direction = "E" Then If Choice = 1 Then FirstBird.Move("E", Time) Else SecondBird.Move("E", Time) End If ElseIf Direction = "WEST" Or Direction = "W" Then If Choice = 1 Then FirstBird.Move("W", Time) Else SecondBird.Move("W", Time) End If Else Valid = False End If End While Console.WriteLine(FirstBird.GetSpecies() & " is currently at " & FirstBird.GetPosition()) Console.WriteLine(SecondBird.GetSpecies() & " is currently at " & SecondBird.GetPosition()) Python Choice = 0 while Choice != 1 and Choice != 2: print("Which bird do you want to move") print("Enter 1 for", FirstBird.GetSpecies(), "is currently at", FirstBird.GetPosition()) Choice = -1 print("Enter 2 for", SecondBird.GetSpecies(), "is currently at", SecondBird.GetPosition()) 1(c)(i) Choice = int(input()) Time = -1 while Time < 0 || Time > 500: Time = int(input("To the nearest minute how long has the bird been flying ")) Valid = False while Valid == False: Valid = True Direction = input("Which direction has the bird been flying, North, South, East or West ").upper() if Direction == "NORTH" or Direction == "N": if Choice == 1: FirstBird.Move("N",Time) else: SecondBird.Move("N",Time) elif Direction == "SOUTH" or Direction == "S": if Choice == 1: FirstBird.Move("S",Time) else: SecondBird.Move("S",Time) elif Direction == "EAST" or Direction == "E": if Choice == 1: FirstBird.Move("E",Time) else: SecondBird.Move("E",Time) elif Direction == "WEST" or Direction == "W": if Choice == 1: FirstBird.Move("W",Time) else: SecondBird.Move("W",Time) else: Valid = False print(FirstBird.GetSpecies(), "is currently at", FirstBird.GetPosition()) print(SecondBird.GetSpecies(), "is currently at", SecondBird.GetPosition()) 1(c)(ii) 1 mark for each: 3 • screenshot showing inputs for one test with correct output • screenshot showing inputs for a second test with correct output • screenshot showing inputs for a third and fourth test with correct output e.g. Test 1: Test 2: Test 3: Test 4:

Mark scheme

2(a) 1 mark each 3 • Creation of 1D array … • … with 20 generated random integers between 0 and 100 (inclusive) … • … all 20 random integers are unique Example program code Java public static void main(String args[]){ Integer[] TheArray = new Integer[20]; Integer Generated; Integer X = 0; Random RandomNumber = new Random(); while(X < 20){ Generated = RandomNumber.nextInt(101); if(Arrays.asList(TheArray).indexOf(Generated) < 0){ TheArray[X] = Generated; X++; } } } VB.NET Dim RandomNumber As Random = New Random() Dim TheArray(19) As Integer Dim Generated As Integer Dim X As Integer = 0 While X < 20 Generated = RandomNumber.Next(0, 100) If Array.IndexOf(TheArray, Generated) < 0 Then TheArray(X) = Generated X = X + 1 End If End While 2(a) Python TheArray = [] TheArray = random.sample(range(0,101),20) 2(b) 1 mark each 3 • Procedure header (and close) taking (array) as parameter • Outputting array contents once … • … on one line with a space between each integer Example program code Java public static void PrintArray(Integer[] DataArray){ String Output = ""; for(Integer X = 0; X < 20; X++){ Output += Integer.toString(DataArray[X]) + " "; } System.out.println(Output); } VB.NET Sub PrintArray(DataArray() As Integer) Dim Output As String = "" For X = 0 To 19 Output = Output + Str(DataArray(X)) + " " Next X Console.WriteLine(Output) End Sub Python def PrintArray(DataArray): Output = "" for Item in DataArray: Output = Output + str(Item) + " " print(Output) 2(c) 1 mark each 5 • Function header (and end) taking (array) parameter and returning a sorted array after sorting • Outer loop … • … inner loop ... • … comparing elements and swapping into ascending order • Sort must work for array of any length i.e. loops for length of parameter array Example program code Java public static Integer[] BubbleSort(Integer[] DataArray){ Boolean Swap = true; Integer Temp; while(Swap){ Swap = false; for(Integer X = 0; X < DataArray.length - 1; X++){ if(DataArray[X] > DataArray[X+1]){ Temp = DataArray[X]; DataArray[X] = DataArray[X + 1]; DataArray[X + 1] = Temp; Swap = true; } } } return DataArray; } 2(c) VB.NET Function BubbleSort(DataArray() As Integer) Dim Swap As Boolean = True Dim Temp As Integer While Swap = True Swap = False For X = 0 To DataArray.Length - 2 If DataArray(X) > DataArray(X + 1) Then Temp = DataArray(X) DataArray(X) = DataArray(X + 1) DataArray(X + 1) = Temp Swap = True End If Next X End While Return DataArray End Function Python def BubbleSort(DataArray): Swap = True while Swap == True: Swap = False for y in range(0, len(DataArray)-1): if DataArray[y] > DataArray[y+1]: DataArray[y], DataArray[y+1] = DataArray[y+1], DataArray[y] Swap = True return DataArray 2(d)(i) 1 mark each 3 • Calling PrintArray() with array as argument • Calling BubbleSort() with array as argument and storing/using return value • Outputting "Sorted" and calling PrintArray() with (returned) array as argument Example program code Java PrintArray(TheArray); Integer[] SortedArray = new Integer[20]; SortedArray = BubbleSort(TheArray); System.out.println("Sorted"); PrintArray(SortedArray); VB.NET PrintArray(TheArray) Dim SortedArray(19) As Integer SortedArray = BubbleSort(TheArray) Console.WriteLine("Sorted") PrintArray(SortedArray) Python PrintArray(TheArray) SortedArray = BubbleSort(TheArray) print("Sorted") PrintArray(SortedArray) 2(d)(ii) 1 mark 1 • Output shows unsorted array of 20 integers between 0 and 100 inclusive before sorting, “Sorted” output, array of the same integers sorting into ascending order. All screenshots will be unique to the candidate 2(e) 1 mark each 6 • Function header (and end) taking four parameters and recursive function written • Calculating middle value • Comparing middle value to data parameter and returning index if equal • If middle is greater than, recursive call with middle –1 for upper • If middle is less than, recursive call with middle + 1 for lower • Checking if not found and returning –1 Example program code Java public static Integer RecursiveBinarySearch(Integer[] DataArray, Integer Lower, Integer Upper, Integer DataToFind){ Integer Middle; if(Upper >= Lower){ Middle = Lower + (Upper - Lower) / 2; if(DataArray[Middle] == DataToFind){ return Middle; }else if(DataArray[Middle] > DataToFind){ return RecursiveBinarySearch(DataArray, Lower, Middle - 1, DataToFind); }else{ return RecursiveBinarySearch(DataArray, Middle + 1, Upper, DataToFind); } }else{ return -1; } } 2(e) VB.NET Function RecursiveBinarySearch(DataArray() As Integer, Lower As Integer, Upper As Integer, DataToFind As Integer) Dim Middle As Integer If Upper >= Lower Then Middle = Lower + (Upper - Lower) \ 2 If DataArray(Middle) = DataToFind Then Return Middle ElseIf DataArray(Middle) > DataToFind Then Return RecursiveBinarySearch(DataArray, Lower, Middle - 1, DataToFind) Else Return RecursiveBinarySearch(DataArray, Middle + 1, Upper, DataToFind) End If Else Return -1 End If End Function Python def RecursiveBinarySearch(DataArray, Lower, Upper, DataToFind): if Upper >= Lower: Middle = Lower + (Upper - Lower) // 2 if DataArray[Middle] == DataToFind: return Middle elif DataArray[Middle] > DataToFind: return RecursiveBinarySearch(DataArray, Lower, Middle - 1, DataToFind) else: return RecursiveBinarySearch(DataArray, Middle + 1, Upper, DataToFind) else: return -1 2(f)(i) 1 mark each 3 • Prompt and input of integer • Call of RecursiveBinarySearch(SortedArray, 0, 19, input) and storing/using return value • Output of "Not found" if –1 returned and output "Found at position" with index returned if found Example program code Java System.out.println("Enter the number to find"); Scanner scanner = new Scanner(System.in); Integer DataToFind = Integer.parseInt(scanner.nextLine()); Integer Location = RecursiveBinarySearch(SortedArray, 0, 19, DataToFind); if(Location == -1){ System.out.println("Not found"); }else{ System.out.println("Found at position " + Location); } VB.NET Console.WriteLine("Enter the number to find ") Dim DataToFind As Integer = Console.ReadLine() Dim Location As Integer = RecursiveBinarySearch(SortedArray, 0, 19, DataToFind) If Location = -1 Then Console.WriteLine("Not found") Else Console.WriteLine("Found at position " & Location) End If Python DataToFind = int(input("Enter the number to find ")) Location = RecursiveBinarySearch(SortedArray, 0, 19, DataToFind) if Location == -1: print("Not found") else: print("Found at position", Location) 2(f)(ii) 1 mark each 2 • screenshot showing smallest number in array input and found message with index 0 and screenshot showing highest number in array input and found message with index 19 • screenshot showing a number not in the array input and an output of "Not found" All screenshots will be unique to the candidate

Mark scheme

3(a) 1 mark each 3 • (global) TreeArray declared as a 2D array with 50 × 3 elements … • … all initialised to –1 • (global) RootPointer initialised to –1 and FreeNode initialised to 0 Example program code Java public static Integer FreeNode; public static Integer RootPointer; public static Integer[][] TreeArray = new Integer[50][3]; public static void main(String args[]){ for(Integer X = 0; X < 50; X++){ TreeArray[X][0] = -1; TreeArray[X][1] = -1; TreeArray[X][2] = -1; } RootPointer = -1; FreeNode = 0; } VB.NET Dim FreeNode As Integer Dim TreeArray(0 To 49, 0 To 2) As Integer Dim RootPointer As Integer Sub Main(args As String()) For X = 0 To 49 TreeArray(X, 0) = -1 TreeArray(X, 1) = -1 TreeArray(X, 2) = -1 Next RootPointer = -1 FreeNode = 0 End Sub 3(a) Python TreeArray = [] for x in range(50): TreeArray.append([-1,-1,-1]) RootPointer = -1 FreeNode = 0 3(b) 1 mark each to max 7 7 • Procedure header (and end) taking one (integer) parameter and storing parameter in array in index TreeArray[FreeNode][1] • Checking if tree is full (FreeNode = 50) and outputting "The tree is full" • Checking if tree is empty (RootPointer = -1 // FreeNode = 0) and if so, storing 0 in RootPointer • (if not empty) Comparing parameter to data at index TreeArray[RootPointer][1] … • … if less than, accessing left node … • … if greater than, accessing right node … • … until location found … • … updating parent node's appropriate pointer • Incrementing FreeNode Example program code Java public static void AddNode(Integer NodeData){ Boolean Placed; Integer CurrentNode; if(FreeNode <= 49){ TreeArray[FreeNode][0] = -1; TreeArray[FreeNode][1] = NodeData; TreeArray[FreeNode][2] = -1; if(RootPointer == -1){ RootPointer = 0; }else{ Placed = false; CurrentNode = RootPointer; while(Placed == false){ if(NodeData < TreeArray[CurrentNode][1]){ if(TreeArray[CurrentNode][0] == -1){ TreeArray[CurrentNode][0] = FreeNode; Placed = true; }else{ 3(b) CurrentNode = TreeArray[CurrentNode][0]; } }else{ if(TreeArray[CurrentNode][2] == -1){ TreeArray[CurrentNode][2] = FreeNode; Placed = true; }else{ CurrentNode = TreeArray[CurrentNode][2]; } } } } FreeNode++; }else{ System.out.println("The tree is full"); } } VB.NET Sub AddNode(NodeData) Dim Placed As Boolean Dim CurrentNode As Integer If FreeNode <= 49 Then TreeArray(FreeNode, 0) = -1 TreeArray(FreeNode, 1) = NodeData TreeArray(FreeNode, 2) = -1 If RootPointer = -1 Then RootPointer = 0 Else Placed = False CurrentNode = RootPointer While Placed = False If NodeData < TreeArray(CurrentNode, 1) Then If TreeArray(CurrentNode, 0) = -1 Then TreeArray(CurrentNode, 0) = FreeNode 3(b) Placed = True Else CurrentNode = TreeArray(CurrentNode, 0) End If Else If TreeArray(CurrentNode, 2) = -1 Then TreeArray(CurrentNode, 2) = FreeNode Placed = True Else CurrentNode = TreeArray(CurrentNode, 2) End If End If End While End If FreeNode = FreeNode + 1 Else Console.WriteLine("The tree is full") End If End Sub Python def AddNode(NodeData): global FreeNode global TreeArray global RootPointer if FreeNode <= 49: TreeArray[FreeNode][0] = -1 TreeArray[FreeNode][1] = NodeData TreeArray[FreeNode][2] = -1 if RootPointer == -1: RootPointer = 0 else: Placed = False CurrentNode = RootPointer while Placed == False: if NodeData < TreeArray[CurrentNode][1]: 3(b) if TreeArray[CurrentNode][0] == -1: TreeArray[CurrentNode][0] = FreeNode Placed = True else: CurrentNode = TreeArray[CurrentNode][0] else: if TreeArray[CurrentNode][2] == -1: TreeArray[CurrentNode][2] = FreeNode Placed = True else: CurrentNode = TreeArray[CurrentNode][2] FreeNode = FreeNode + 1 else: print("The tree is full") 3(c) 1 mark each to max 4 4 • Opening the file to read and closing the file in an appropriate place • Looping 50 times/through file/through each line/until EOF … • … reading in each line … • … calling AddNode() with each value read in • Exception handling try, catch, except with appropriate message Example program code Java Integer Line; String ReadData; try{ FileReader f = new FileReader("TreeData.txt"); try{ BufferedReader Reader = new BufferedReader(f); ReadData = Reader.readLine(); while (ReadData != null){ Line = Integer.parseInt(ReadData); AddNode(Line); ReadData = Reader.readLine(); } Reader.close(); }catch(IOException ex){ } }catch(FileNotFoundException e){ System.out.println("File not found"); } 3(c) VB.NET Try Dim FileReader As New System.IO.StreamReader("TreeData.txt") While Not FileReader.EndOfStream AddNode(FileReader.ReadLine()) End While FileReader.Close() Catch ex As Exception Console.WriteLine("Cannot open file") End Try Python try: File= open("TreeData.txt") for Line in File: AddNode(int(Line.strip())) File.close() except: print("Error cannot open file") 3(d) 1 mark each 5 • Procedure header (and end) and with exception handling for writing to file: try, catch, except with appropriate message • Opening the file (Tree.txt) to write and closing the file in appropriate place • Looping through each element in array … • … creating correct string • … writing each string to the file Example program code Java public static void WriteAllToFile(){ File TheFile = new File("Tree.txt"); String Line; try{ FileWriter FW = new FileWriter(TheFile, true); for(Integer X = 0; X < 50; X++){ Line = TreeArray[X][0] + "," + TreeArray[X][1] + "," + TreeArray[X][2]; FW.write(Line); FW.write("\n"); } FW.close(); }catch(IOException ex){ System.out.println("Cannot open file"); } } 3(d) VB.NET Sub WriteAllToFile() Dim FileWriter As IO.StreamWriter = New IO.StreamWriter("Tree.txt", False) Dim Line As String Try For x = 0 To 49 Line = TreeArray(x, 0) & "," & TreeArray(x, 1) & "," & TreeArray(x, 2) FileWriter.WriteLine(Line) Next FileWriter.Close() Catch ex As Exception Console.WriteLine("Cannot open or write to file") End Try End Sub Python def WriteAllToFile(): try: File = open("Tree.txt","a+") for x in range(0, 50): Line = str(TreeArray[x][0]) + "," + str(TreeArray[x][1])+ "," + str(TreeArray[x][2]) + "\n" File.write(Line) File.close() except: print("Cannot write to file") 3(e)(i) 1 mark for calling WriteAllToFile() 1 Example program code Java WriteAllToFile(); VB.NET WriteAllToFile() Python WriteAllToFile() 3(e)(ii) 1 mark for a screenshot that shows correct data stored, each node on a new line (in correct format). 1 The screenshot must include the filename. e.g.