Take-Home Lab #02 CS1020 – DATA STRUCTURES AND ALGORITHMS 1 AY SEMESTER 2 1

Problem 1 Tournament 2

 Simulate a tournament: Two important numbers: M (the number of participants) and N (the number of rounds). Assign initial seat numbers and scores for each participant. Just simulate the tournament as given in the problem description. 3

 For each Participant, we need to implement: Setter method for seat number Setter method for multiplier Getter methods Method for calculating new seat number Method for adding points Tournament 4

 Appropriate attributes:  name: String  cardNumber: int  score: int  seatNumber: int Class: Participant Tournament 5

 What you will need in order to ease the process: Array of Participants Use the participant’s seat number as the index. You can easily retrieve Participants by having the seat number and easily modify the seat number of a participant Tournament 6

 Just simulate the process of the tournament and you should be fine.  Use the remainder/modulo operator (%) in Java to get the new seat number of a Participant to avoid “overflow”  After that, just iterate through all participants to find out who has the maximum score. Tournament 7

Problem 2 File 8

 Simulate a file manager system: Create files and folders Delete a file from a folder Move a file to another folder Calculate the size of a folder Find the folder with the largest size File 9

FolderFile File Manager File 10

File Manager Tutorials Take-Home Labs Sit-In Labs filenameOne tournament file restaurant File 11

File Manager FolderFile 12

File FileManager: public class FileManager() File: class File(String name, int fileSize, String folderName) Folder: class Folder(String name) 13

FileManager Keeps a list of all folders currently in the system Reads and executes the queries Folder Some tips: Have a method to get the size of the folder. Instead of having a setter to set the list of files, create an “addFile” method that acts as a “setter” of a file being added to the folder. Whenever you add a file to a folder, change the folderName attribute of that file File Contains information about: The file name The file size The folder in which the file is in File 14

public void addFile(File newFile) { this.listOfFiles.add(newFile); newFile.setFolderName(this.getName()); } Folder public int getSize() { int size = 0; for (File f : listOfFiles) { //read as: for every File f in listOfFiles size += f.getSize(); } return size; } File 15

FileManager ?  How do I get the Folder (or File) object, given its name? ArrayList HashMap VS Need to iterate through the list. Elaborated further in the Restaurant problem discussion Fast and Easy File 16

 How do I use HashMap? HashMap HashMap hashMapName = new HashMap (); public class FileManager { private HashMap fileMapping; private HashMap folderMapping; private ArrayList listOfFolders; public FileManager() { this.fileMapping = new HashMap (); this.folderMapping = new HashMap (); this.listOfFolders = new ArrayList (); } … //etc. } FileManager File 17

Adding a Key-Value Mapping folderMapping.put(folderName, newFolder); Value Retrieval using a Key Folder retrievedFolder = folderMapping.get(folderName); folderName is a String while newFolder is a Folder folderName is a string containing the name of the folder retrievedFolder 18

Problem 3 Restaurant 19

 Manage a restaurant and perform these types of queries: Assign a specific table to a specific group Assign the lexicographically-smallest available table to a specific group A specific group leaves the restaurant Prints the name of the table that a specific group is currently in Prints the name of the group of a specific table Problem Description 20

Restaurant Group Table Group Problem Illustration 21

Restaurant GroupTable Contains Has Uses Relationship Between Entities 22

Class Overview Restaurant Keeps a list of all tables and groups currently in the restaurant Reads and executes the queries Table Contains information about: Capacity of the table The group that is assigned to it The status of the table Its name Group Contains information about: The number of people The assigned table The group’s name 23

 Class Restaurant Class Overview Restaurant -tables : ArrayList -groups : ArrayList +//methods  Class Table Table -name : String -capacity : int -isOccupied : Boolean -currentGroup : Group +getName() : String +reset() : void -toggle() : void …  Class Group Group -name : String -capacity : int -currentTable : Table +getName() : String +getCapacity() : int +getTable() : Table … No need getter-setter for Restaurant; Restaurant acts as a “Controller” 24

public void setGroup(Group g) { this.currentGroup = g; this.toggle(); } public void reset() { this.currentGroup = null; this.toggle(); } private void toggle() { this.isOccupied = !this.isOccupied; } Private Helper in Table 25

Constructors Restaurant: public class Restaurant() Group: class Group(String name, int numOfPeople, Table assignedTable) Table: class Table(String name, int capacity) Some questions to ponder: When do we create a new group?  When we can assign it a table. A group cannot “queue”, i.e. if it could not be assigned a table, it leaves the restaurant. When do we add tables (or groups) to the list in Restaurant?  After the creation of each object. When do we remove tables (or groups) from the list in Restaurant?  You remove a group from the list when it leaves the restaurant. You do not remove tables from the list. 26

 Some tips for processing the queries:  Perform all logical operations in the Restaurant class  Avoid the use of static variables and methods  The methods in the table and group class are only for operations that modifies or returns their own attributes. These operations are called by the Restaurant class. E.g:  getName(): returns the name of the table (or group)  reset(): resets a table back to vacant (and toggle the status of the table)  We define helper methods in Restaurant as we go along, e.g:  getTableBasedOnName(String tableName): returns the Table with the name tableName, returns null if not found  getValidLexiSmallestTable(int numOfPeople): returns the lexicographically smallest Table that fits the group with numOfPeople. Useful Tips 27

How to avoid static In the Restaurant Class  What most of you did (in your take-home lab submissions): public static void main(String[] args) { //your code } public static Table getTableBasedOnName(String name) { //implementation }  How to avoid static: public static void main(String[] args) { Restaurant myRestaurant = new Restaurant(); myRestaurant.run(); } public void run() { //your code (treat this as “main”) } public Table getTableBasedOnName(String name) { //implementation } 28

The Run Method (in Restaurant) public void run() { Scanner sc = new Scanner(System.in); int N = sc.nextInt(); sc.nextLine(); readAndStoreTables(sc, N); int Q = sc.nextInt(); sc.nextLine(); executeQueries(sc, Q); } 29

Read and Store Tables private void readAndStoreTables(Scanner sc, int N) { for (int i = 0; i < N; i++) { //reads the input and split it if //a blank space (" ") is found String[] split = sc.nextLine().split(" "); //store table information into local variables String tableName = split[0]; int capacity = Integer.parseInt(split[1]); //create new table object and store it into //the list of tables Table newTable = new Table(tableName, capacity); tables.add(newTable); } 30

Execute Queries private void executeQueries(Scanner sc, int Q) { for (int i = 0; i < Q; i++) { String[] splittedInput = sc.nextLine().split(" "); int input = Integer.parseInt(splittedInput[0]); //execute queries based on type //you can also use switch-case if (input == 1) { assignFavoriteTable(splittedInput); } else if (input == 2) { assignLexiSmallestTable(splittedInput); } else if (input == 3) { leaveRestaurant(splittedInput); } else if (input == 4) { printOccupiedTable(splittedInput); } else { printCurrentGroupName(splittedInput); } 31

 Query 1 Query 1: Assign group to specific table private void assignFavoriteTable(String[] splittedInput) { String groupName = splittedInput[1]; int numOfPeople = Integer.parseInt(splittedInput[2]); String tableName = splittedInput[3]; Table favTable = getTableBasedOnName(tableName); } If table is not null and can assign*  create group and assign table If not  print “not possible” * Can assign if: 1. The capacity of favTable is at least numOfPeople 2. favTable is currently vacant 32

 Helper Method (Reusable for queries 1 and 5) /* for sit-in labs, this is a good example of pre- and post- condition * pre-condition: The arraylist of tables has been initialized and tables * have been stored properly * * post-condition: Returns the table with name tableName and null if there * is no such table * * description: iterates through the list of tables and return the most * appropriate table based on tableName. Returns null if no such table is * found */ private Table getTableBasedOnName(String tableName) { } Helper Method: getTableBasedOnName -Loop through the list of tables -If the current table’s name matches tableName, return that Table and stop the loop. Why can we stop? -After finish iterating and no table is found: return null 33

private void assignLexiSmallestTable(String[] splittedInput) { String groupName = splittedInput[1]; int numOfPeople = Integer.parseInt(splittedInput[2]); Table assigned = getValidTable(numOfPeople); }  Query 2 Query 2: Assign group to a table If table is not null*  create group and assign table If null (we don’t find a table that fits)  print “not possible” * We don’t need to check if it is assignable as in query 1 since we do the checking inside getValidTable(). Why?  we will iterate through all tables and find the lexicographically smallest valid table. Hence, as we iterate, we also check its validity.  Why do we need to iterate through all tables? Think! 34

/* * pre-condition: ??? * post-condition: ??? * description: ??? */ private Table getValidTable(int numOfPeople) { }  Helper Method Helper Method: getValidTable -Loop through the list of tables while keeping the current lexi- smallest and valid table in a local variable -For each table: check its validity. If it’s invalid, skip. If it’s valid, compare with the current lexi-smallest table. If this new table is lexicographically smaller, update the local variable that keeps the table. -Return the lexi-smallest available table (if it exists) or null otherwise 35

 Query 3 Query 3: A group leaves the restaurant private void leaveRestaurant(String[] splittedInput) { String groupName = splittedInput[1]; Group currentGroup = getGroupBasedOnName(groupName); } If currentGroup is not null  reset its table and assign null as currentGroup ’s table and remove currentGroup from the list of groups inside the restaurant If null (there is no such group)  do nothing The implementation of getGroupBasedOnName is similar to getTableBasedOnName. This helper is useful for Queries 3 and 4. 36

 Query 4 Query 4 : Print the current group’s table Why?  we only add groups to the list when we assign it a table  when a group leaves, we remove it from the list of groups private void printOccupiedTable(String[] splittedInput) { String groupName = splittedInput[1]; Group currentGroup = getGroupBasedOnName(groupName); } If currentGroup is not null  print its table name. We do not need to check if it has a table or not. Why*? If null  print “invalid” 37

 Query 5 private void printCurrentGroupName(String[] splittedInput) { String tableName = splittedInput[1]; Table curTable = getTableBasedOnName(tableName); } Query 5 : Print the current group of the table If curTable is not null and it is occupied  print the occupying group’s name. Else  print “invalid” 38

End Of File Any Questions? 39