Computer Science 9618/41 October/November 2025: question paper and mark scheme

Mark scheme

1(a) 1 mark each 2 • (Global) 1D array initialised with 30 null values • (Global) TopofStack initialised with –1 Example program code Java public static Integer[] Stack = new Integer[30]; public static Integer TopOfStack; public static void main(String args[]){ for(Integer X = 0; X < 30; X++){ Stack[X] = null; } TopOfStack = -1; } VB.NET Dim Stack(29) As Integer Dim TopOfStack As Integer Sub Main(args As String()) For x = 0 To 29 Stack(x) = Nothing Next TopOfStack = -1 End Sub Python Stack = [None for x in range(30)] TopOfStack = -1 1(b) 1 mark each 4 • Function header (and end) taking one parameter, returning Boolean in all instances • Checking if stack is full (TopOfStack = 29) and, if it is, returning FALSE • Incrementing TopofStack • (Otherwise) Storing parameter in incremented TopOfStack position and returning TRUE Example program code Java public static Boolean Push(Integer DataToPush){ if(TopOfStack < 29){ TopOfStack++; Stack[TopOfStack] = DataToPush; return true; } return false; } VB.NET Function Push(DataToPush) If TopOfStack < 29 Then TopOfStack = TopOfStack + 1 Stack(TopOfStack) = DataToPush Return True End If Return False End Function 1(b) Python def Push(DataToPush): global Stack global TopOfStack if TopOfStack < 29: TopOfStack = TopOfStack + 1 Stack[TopOfStack] = DataToPush return True else: return False 1(c) 1 mark each 4 • Function header (and end) returning integer in all cases • Checking if stack empty (TopofStack = –1) and returning -999 when true • (Otherwise) Accessing and returning item at TopOfStack (before it's decremented) • Decrementing TopofStack Example program code Java public static Integer Pop(){ Integer DataReturn; if(TopOfStack == -1){ return -999; } DataReturn = Stack[TopOfStack]; TopOfStack--; return DataReturn; } VB.NET Function Pop() If TopOfStack = -1 Then Return -999 Else Dim DataReturn As Integer = Stack(TopOfStack) TopOfStack = TopOfStack - 1 Return DataReturn End If End Function 1(c) Python def Pop(): global Stack global TopOfStack if TopOfStack == -1: return -999 else: DataReturn = Stack[TopOfStack] TopOfStack = TopOfStack - 1 return DataReturn 1(d) 1 mark each 4 • Looping 40 times • Generating random number between 0 and 1000 inclusive inside the loop • Calling Push() with each random number and storing/using return value … … if return value is FALSE output Stack full and breaking out of loop Example program code Java for(Integer X = 0; X < 40; X++){ Pushed = Push(RandomNumber.nextInt(1001)); if(Pushed == false){ System.out.println("Stack full"); X = 40; } } VB.NET For x = 0 To 39 Pushed = Push(RandomNumber.Next(0, 1000)) If Pushed = False Then Console.WriteLine("Stack full") x = 40 End If Next Python for x in range(40): Pushed = Push(random.randint(0,1000)) if Pushed == False: print("Stack full") break 1(e) 1 mark each 4 • Procedure header (and end) and output of highest and lowest include appropriate messages • Calls Pop() until there are no items left in stack (return value = –999 // TopOfStack = -1) and storing/using return values • Finds and outputs highest value from returned values • Finds and outputs lowest value from returned values Example program code Java public static void FindValues(){ Integer Highest; Integer Lowest; Highest = Pop(); Lowest = Highest; Integer ReturnValue = Highest; while(ReturnValue != -999){ if(ReturnValue > Highest){ Highest = ReturnValue; } if(ReturnValue < Lowest){ Lowest = ReturnValue; } ReturnValue = Pop(); } System.out.println("The highest value is " + Highest + " and the lowest value is " + Lowest); } 1(e) VB.NET Sub FindValues() Dim Highest, Lowest As Integer Highest = Pop() Lowest = Highest Dim ReturnValue As Integer = Highest While ReturnValue <> -999 If ReturnValue > Highest Then Highest = ReturnValue End If If ReturnValue < Lowest Then Lowest = ReturnValue End If ReturnValue = Pop() End While Console.WriteLine("The highest value is " & Highest & " and the lowest value is " & Lowest) End Sub Python def FindValues(): Highest = Pop() Lowest = Highest ReturnValue = Lowest while(ReturnValue != -999): if ReturnValue > Highest: Highest = ReturnValue if ReturnValue < Lowest: Lowest = ReturnValue ReturnValue = Pop() print("The highest value is", Highest, "and the lowest value is", Lowest) 1(f)(i) 1 mark for calling FindValues() 1 Example program code Java FindValues(); VB.NET FindValues() Python FindValues() 1(f)(ii) 1 mark for a screenshot of output showing 1 Stack full output once Lowest value output in an appropriate message Highest value output in an appropriate message Lowest and Highest must be 0–1000 inclusive

Mark scheme

2(a)(i) 1 mark each 4 • Class header (and end) • Declaration of 2 private attributes with correct data types • Constructor header (and end) within class with 2 parameters … • … assigning parameters to attributes Example program code Java class Train{ private String Number; private Integer Route; public Train(String pNumber, Integer pRoute){ Number = pNumber; Route = pRoute; }} VB.NET Class Train Private TrainIDNumber As String Private Route As Integer Sub New(pNumber, pRoute) TrainIDNumber = pNumber Route = pRoute End Sub End Class Python class Train(): def __init__(self, pNumber, pRoute): self.__TrainIDNumber = pNumber #string self.__Route = pRoute #integer 2(a)(ii) 1 mark each 3 • One get method header (and end) with no parameter … • … returning correct attribute • Second correct get method Example program code Java public String GetTrainNumber(){ return Number; } public Integer GetRoute(){ return Route; } VB.NET Function GetTrainIDNumber() Return TrainIDNumber End Function Function GetRoute() Return Route End Function Python def GetTrainIDNumber(self): return self.__TrainIDNumber def GetRoute(self): return self.__Route 2(b) 1 mark each 2 • One instance of train with correct arguments and stored in a variable/structure • Remaining three instances correct Example program code Java Train FirstTrain = new Train("12ADV", 134); Train SecondTrain = new Train("33ART", 20); Train ThirdTrain = new Train("9FKF", 3); Train FourthTrain = new Train("21VBC", 24) VB.NET Dim FirstTrain As Train = New Train("12ADV", 134) Dim SecondTrain As Train = New Train("33ART", 20) Dim ThirdTrain As Train = New Train("9FKF", 3) Dim FourthTrain As Train = New Train("21VBC", 24) Python FirstTrain = Train("12ADV",134) SecondTrain = Train("33ART",20) ThirdTrain = Train("9FKF",3) FourthTrain = Train("21VBC",24) 2(c)(i) 1 mark each 3 • Class header (and end) with four private attributes with appropriate data types • Constructor header (and end) within class taking 2 parameters … • … assigning parameters to attributes, initialising NumberTrains to 0, initialising Trains to an empty array Example program code Java class Station{ private String StationID; private Integer NumberPlatforms; private Train[] Trains = new Train[10]; private Integer NumberTrains; public Station(String pID, Integer pNumberOfPlatforms){ StationID = pID; NumberPlatforms = pNumberOfPlatforms; NumberTrains = 0; }} VB.NET Class Station Private StationID As String Private NumberPlatforms As Integer Private Trains(9) As Train Private NumberTrains As Integer Sub New(pID, pNumberOfPlatforms) StationID = pID NumberPlatforms = pNumberOfPlatforms NumberTrains = 0 End Sub End Class 2(c)(i) Python class Station(): def __init__(self, pID, pNumberOfPlatforms): self.__StationID = pID #string self.__NumberPlatforms = pNumberOfPlatforms #integer self.__Trains = [] #train 10 elements self.__NumberTrains = 0 #integer 2(c)(ii) 1 mark each 4 • Method header (and close) taking one Train parameter • Checking if all platforms are full and returning FALSE • (Otherwise) Storing parameter in array Trains … • … incrementing NumberTrains and returning True Example program code Java public Boolean AddTrain(Train NewTrain){ if(NumberTrains >= NumberPlatforms){ return false; } Trains[NumberTrains] = NewTrain; NumberTrains++; return true; } VB.NET Function AddTrain(NewTrain) If NumberTrains >= NumberPlatforms Then Return False End If Trains(NumberTrains) = NewTrain NumberTrains = NumberTrains + 1 Return True End Function Python def AddTrain(self, NewTrain): if self.__NumberTrains >= self.__NumberPlatforms: return False else: self.__Trains.append(NewTrain) self.__NumberTrains += 1 return True 2(c)(iii) 1 mark each 6 • Method header (and close) and returning a string in all cases • Checking if no trains and returning "There are no trains" • (Otherwise) Looping through each train in the station … • … accessing train ID number and route number using get methods • … creating a string with ID number and route number for each train • … returning correctly formatted string Example program code Java public String GetTrains(){ if(NumberTrains == 0){ return "There are no trains"; } String OutputLine = "The trains at station " + StationID + " are: \n"; for(Integer x =0; x < NumberTrains; x++){ OutputLine = OutputLine + Trains[x].GetTrainNumber() + " on route number " + Trains[x].GetRoute() + "\n"; } return OutputLine; } VB.NET Function GetTrains() If NumberTrains = 0 Then Return "There are no trains" End If Dim OutputLine As String = "The trains at station " & StationID & " are:" & vbNewLine For x = 0 To NumberTrains - 1 OutputLine = OutputLine & Trains(x). GetTrainIDNumber() & " on route number " & Trains(x).GetRoute() & vbNewLine Next Return OutputLine End Function 2(c)(iii) Python def GetTrains(self): if self.__NumberTrains == 0: return "There are no trains" OutputLine = "The trains at station " + self.__StationID + " are: \n" for x in range(self.__NumberTrains): OutputLine = OutputLine + self.__Trains[x]. GetTrainIDNumber() + " on route number " + str(self.__Trains[x].GetRoute()) + "\n" return OutputLine 2(d)(i) 1 mark each 2 • One instance of Station created with correct arguments and stored • Second correct instance and stored Example program code Java Station SouthStation = new Station("STH", 2); Station NorthStation = new Station("NTH", 1); VB.NET Dim SouthStation As Station = New Station("STH", 2) Dim NorthStation As Station = New Station("NTH", 1) Python SouthStation = Station("STH",2) NorthStation = Station("NTH",1) 2(d)(ii) 1 mark each 4 • Calling AddTrain for 3 correct trains for station STH once • Calling AddTrain for 1 correct train for station NTH once • Outputting "Station is full" if any return value is FALSE • Calling GetTrains() for both stations and outputting return values Example program code Java Boolean ReturnValue = SouthStation.AddTrain(FirstTrain); if(ReturnValue == false) { System.out.println("Station is full"); } ReturnValue = SouthStation.AddTrain(SecondTrain); if(ReturnValue == false) { System.out.println("Station is full"); } ReturnValue = SouthStation.AddTrain(ThirdTrain); if(ReturnValue == false) { System.out.println("Station is full"); } ReturnValue = NorthStation.AddTrain(FourthTrain); if(ReturnValue == false) { System.out.println("Station is full"); } System.out.println(SouthStation.GetTrains()); System.out.println(NorthStation.GetTrains()); VB.NET Dim ReturnValue As Boolean = SouthStation.AddTrain(FirstTrain) If ReturnValue = False Then Console.WriteLine("Station is full") End If ReturnValue = SouthStation.AddTrain(SecondTrain) If ReturnValue = False Then 2(d)(ii) Console.WriteLine("Station is full") End If ReturnValue = SouthStation.AddTrain(ThirdTrain) If ReturnValue = False Then Console.WriteLine("Station is full") End If ReturnValue = NorthStation.AddTrain(FourthTrain) If ReturnValue = False Then Console.WriteLine("Station is full") End If Console.WriteLine(SouthStation.GetTrains()) Console.WriteLine(NorthStation.GetTrains()) Python ReturnValue = SouthStation.AddTrain(FirstTrain) if ReturnValue == False: print("Station is full") ReturnValue = SouthStation.AddTrain(SecondTrain) if ReturnValue == False: print("Station is full") ReturnValue = SouthStation.AddTrain(ThirdTrain) if ReturnValue == False: print("Station is full") ReturnValue = NorthStation.AddTrain(FourthTrain) if ReturnValue == False: print("Station is full") print(SouthStation.GetTrains()) print(NorthStation.GetTrains()) 2(d)(iii) 1 mark each, screenshot(s) showing: 2 • One output of "Station is full" • Output of correct data for both stations (in correct format) e.g.

Mark scheme

3(a) 1 mark each 2 • Class header (and end) and constructor header (and end) in class • Constructor takes two parameters and stores each in attributes Example program code Java class Record{ public Integer Key; public String Data; public Record(Integer pKey, String pData){ Key = pKey; Data = pData; } } VB.NET Class Record Dim Key As Integer Dim Data As String Sub New(pKey, pData) Key = pKey Data = pData End Sub End Class Python class Record: def __init__(self, pKey, pData): self.Key = pKey #integer self.Data = pData #string 3(b) 1 mark each 2 • 2D array of 100 × 10 elements of type Record • Procedure InitialiseHashTable() header (and end) and initialises each element in the 2D array to an empty/null record in procedure Example program code Java public static Record[][] HashTable = new Record[100][10]; public static void InitialiseHashTable(){ Record EmptyRecord = new Record(-1,"-1"); for(Integer X = 0; X < 100; X++){ for(Integer Y = 0; Y < 10; Y++){ HashTable[X][Y] = EmptyRecord; } } } VB.NET Dim HashTable(99, 9) As Record Sub InitialiseHashTable() Dim EmptyRecord As Record = New Record(-1, "") For X = 0 To 99 For Y = 0 To 9 HashTable(X, Y) = EmptyRecord Next Next End Sub Python HashTable = [] def InitialiseHashTable(): global HashTable HashTable = [[Record(-1,"")]*10 for i in range(100)] 3(c) 1 mark each 2 • Function header (and end) taking one parameter and returning calculated hash • …. hash calculated correctly from parameter Example program code Java public static Integer Hash(Integer TheKey){ return(TheKey % 100); } VB.NET Function Hash(Key) Return Key Mod 100 End Function Python def Hash(Key): return Key % 100 3(d) 1 mark each 4 • Procedure header (and end) taking one Record parameter • Calling Hash() using key from parameter and storing/using return value • Accessing HashTable[return][0] and storing parameter if no collision … … if collision: iterating through 2 nd dimension to find empty index and store parameter in that position Example program code Java public static void InsertData(Record RecordData){ Integer HashValue = Hash(RecordData.Key); for(Integer X = 0; X < 10; X++){ if(HashTable[HashValue][X].Key.equals(-1)){ HashTable[HashValue][X] = RecordData; X = 10; } } } VB.NET Function InsertData(RecordData) Dim HashValue As Integer = Hash(RecordData.Key) For X = 0 To 9 If HashTable(HashValue, X).Key = -1 Then HashTable(HashValue, X) = RecordData X= 10 End If Next X End Function 3(d) Python def InsertData(RecordData): global HashTable HashValue = Hash(RecordData.Key) for X in range(0, 10): if HashTable[HashValue][X].Key == -1: HashTable[HashValue][X] = RecordData 3(e) 1 mark each to max 5 5 • Procedure header (and end), opening file and closing file (in appropriate place) • Iterating through each line in file // reading each line in from file • Splitting each line read in by comma … • … creating Record object with each key and data as arguments … • … calling InsertData() with each object • Try, catch with appropriate output and all file access within try Example program code Java public static void ReadData(){ String[] Data = new String[3]; Integer NewKey; Integer NewItem1; Integer NewItem2; Record TheRecord; try{ FileReader File = new FileReader("HashTableData.txt"); try{ BufferedReader Reader = new BufferedReader(File); String Line= Reader.readLine(); while (Line != null){ Line = Line.replace("\n",""); Data = Line.split(","); TheRecord = new Record(Integer.parseInt(Data[0]), Data[1]); InsertData(TheRecord); Line= Reader.readLine(); } Reader.close(); }catch(IOException ex){} }catch(FileNotFoundException e){System.out.println("File not found");} } 3(e) VB.NET Sub ReadData() Dim Line As String Dim Data(3) As String Dim TheRecord As Record Dim FileReader As New System.IO.StreamReader("HashTableData.txt") While Not FileReader.EndOfStream Line = FileReader.ReadLine() Data = Split(Line, ",") TheRecord = New Record(Integer.Parse(Data(0)), Data(1)) InsertData(TheRecord) End While FileReader.Close() End Sub Python def ReadData(): global HashTable File = open("HashTableData.txt") for Line in File: Data = Line.strip() Data = Line.split(",") InsertData(Record(int(Data[0]), Data[1])) File.close() 3(f) 1 mark each 5 • Function header (and end) taking one parameter and returning string in all cases • Calling Hash() with parameter and storing/using return value • Iterating through 2 nd dimension at HashTable[return value] and comparison to parameter … • … returning data if found/equal • … returning "Not found" if not found by the end of the dimension Example program code Java public static String GetRecord(Integer Key){ Integer HashValue = Hash(Key); for(Integer X = 0; X < 10; X++){ if(HashTable[HashValue][X].Key.equals(Key)){ return(HashTable[HashValue][X].Data); } } return "Not found"; } VB.NET Function GetRecord(Key) Dim HashValue As Integer = Hash(Key) For X = 0 To 9 If HashTable(HashValue, X).Key = Key Then Return HashTable(HashValue, X).Data End If Next X Return "Not found" End Function 3(f) Python def GetRecord(Key): global HashTable HashValue = Hash(Key) for X in range(0, 10): if HashTable[HashValue][X].Key == Key: return HashTable[HashValue][X].Data return "Not found" 3(g)(i) 1 mark each 3 • Calling InitialiseHashTable() then ReadData() • Taking five (integer) inputs • Calling GetRecord() with each input and outputting return value Example program code Java public static void main(String args[]){ InitialiseHashTable(); ReadData(); Scanner scanner = new Scanner(System.in); for(Integer X = 0; X < 5; X++){ System.out.println("Enter key field"); System.out.println(GetRecord(Integer.parseInt(scanner.nextLine()))); } } VB.NET Sub Main(args As String()) InitialiseHashTable() ReadData() For X = 0 To 5 Console.WriteLine("Enter key field") Console.WriteLine(GetRecord(Console.ReadLine())) Next End Sub 3(g)(i) Python InitialiseHashTable() ReadData() for x in range(5): Key = int(input("Enter key field ")) print(GetRecord(Key)) 3(g)(ii) 1 mark each for screenshot(s) showing 2 • Input of the 4 integers and matching word output 528 permission 1128 peace 1828 precedent 1062 up • Input of 39 and output of Not found e.g.