Question

Purpose

• To learn how to use the JCF classes (HashSet, HashMap, TreeSet, TreeMap).
  • You do not need to implement these classes.
• To practice using the StringBuilder class to reduce runtime when working with Strings.

Time Estimate

4-5 hours to complete.

Background

You have been given the following:

Code

• setAndMaps.java

Input files

• imdb.txt
• sight_and_sound.txt
• 3_lists.txt

Sample output

• output_intersection.txt
• output_frequent.txt
• output_groupByNumChars.txt

The sample output is produced for the provided main function; mainly, the following cases:

// intersection
System.out.println(setAndMaps.intersection(list1, list2));

// frequent
System.out.println(setAndMaps.frequent(list3, 3));

// groupByNumChars
System.out.println(setAndMaps.groupByNumChars(list2));

Problem Statement

Three of the methods in setAndMaps.java are incomplete. Write the code so it works correctly. You should only code in one file, setAndMaps.java.

Do not change the method signatures. Each method should return the output as a String.

Code Structure

public static List getList(String filename){};

• This method has been done for you.
  • It takes a filename as a parameter and returns a List of movies.
• Each file contains one movie per line.
  • 3_lists.txt has duplicates because it contains 3 lists
  • the other files do not have duplicates

public static String intersection(List list1, List list2){};

• Return all movies that occur in both lists as a String.
  • Your output MUST be ordered alphanumerically (from a-z, 0-9).
• The expected runtime must be O(nlogn) where n is the total number of movies in the lists.
• Use a HashSet to store one of the lists, so you can search the HashSet efficiently.
  • You may assume that the expected runtime of searching or inserting into a hash table is O(1).
• Do not call the list's contains method, because it is too slow.
• Return all entries (do not deduplicate your result).

public static String frequent(List list, int k){};

• Return all movies in the list that occur at least k times as a String.
  • Your output MUST be ordered alphanumerically (from a-z, 0-9).
• The output String will contain the movie followed by the number of occurrences in parentheses, as in the sample output.
• The expected runtime must be O(nlogn) where n is the total number of movies in the list.
• Use a HashMap to count occurrences
  • the key is the movie
  • the value is the number of occurrences
• For each movie, check if it's a key in the map.
  • If it is, update its value.
  • Otherwise add a new entry to the map.
• Then iterate through the map and print the frequent movies.
  • See UsingSetsMaps for an example of how use a for-each loop with a map.

public static String groupByNumChars(List list){};

• Return all movies in the list, grouped by number of characters, as a String.
  • All movies with the same number of characters should be printed on the same line
  • Movies with fewer characters should be printed first.
  • Your output MUST be ordered alphanumerically (from a-z, 0-9).

Advice

• There is more than one way to solve this problem, but one way is to use a map.
  • The key is the number of characters, and the value is a list of movies with that number of characters.
  • You can declare it like this:

Map> map = new ... // Choose the appropriate map class

• For each movie, you can use the String class's length function to get the number of characters.

  • If the map doesn't already have an entry for this length, create a new entry
    • use the map's put method
  • If the map already has an entry for this length:
    • first call the map's get method (which returns a reference to a list)
    • then add the movie to the list

• Do not use a single String to store more than one movie, because it will slow down the runtime

  • a StringBuilder is fine.

Requirements

• The program takes in text files that are then converted to lists. Your solutions will operate on the parameterized lists.

• The code must properly complete the setAndMaps.java class and work with the provided Main.java class.

• All functions in the setAndMaps.java class MUST be implemented.

• All code you write should exist solely in the specified methods and additional helper functions. NO CODE SHOULD BE ADDED TO THE MAIN FUNCTION

• Base your code on the given template. Any code not adhering to the given template may work, but may not pass all tests upon submission.

import java.io.FileNotFoundException;
import java.io.FileReader;
import java.util.ArrayList;
import java.util.Collections;
import java.util.Scanner;

class Main {
   // Returns a List of all movies in the specified file (assume there is one movie per line).
   public static ArrayList getList(String filename) {
   ArrayList list = new ArrayList<>();
   try (Scanner in = new Scanner(new FileReader(filename))) {
   while (in.hasNextLine()) {
   String line = in.nextLine();
   list.add(line);
   }
   } catch (FileNotFoundException e) {
   e.printStackTrace();
   }
   return list;
   }
   public static void main(String[] args) {
       ArrayList list1 = getList("imdb.txt");
       ArrayList list2 = getList("sight_and_sound.txt");
       ArrayList list3 = getList("3_lists.txt");

//Sort lists
Collections.sort(list1);
Collections.sort(list2);
Collections.sort(list3);
  
       System.out.println("***\nintersection\n***");
       System.out.println(setAndMaps.intersection(list1, list2));

       System.out.println("***\nfrequent\n***");
       System.out.println(setAndMaps.frequent(list3, 3));

       System.out.println("***\ngroupByNumChars\n***");
       System.out.println(setAndMaps.groupByNumChars(list2));
   }
}

import java.util.*;

BELOW IS WHERE WE DO THE CODE

public class setAndMaps {

// Prints all movies that occur in both lists.
public static String intersection(List<String> list1, List<String> list2) {
//Add code below
return "";
}

// Prints all movies in the list that occur at least k times
// (print the movie followed by the number of occurrences in parentheses).
public static String frequent(List<String> list, int k) {
//Add code below
return "";
}

// Prints all movies in the list, grouped by number of characters.
// All movies with the same number of characters are printed on the same line.
// Movies with fewer characters are listed first.
public static String groupByNumChars(List<String> list) {
//Add code below
return "";
}
}

Answer 1

• import java.io.FileNotFoundException;
  import java.io.FileReader;
  import java.util.ArrayList;
  import java.util.Collections;
  import java.util.Scanner;

  class Main {
     //Array list of movies
      public static ArrayList<String> getList(String filename) {
          ArrayList<String> arrayList = new ArrayList<>();
          try (Scanner scanner = new Scanner(new FileReader(filename))) {
              while (scanner.hasNextLine()) {
                  String line = scanner.nextLine();
                  arrayList.add(line);
              }
          } catch (FileNotFoundException exception) {
              exception.printStackTrace();
          }
          return arrayList;
      }
      //main method
      public static void main(String[] args) {
          ArrayList<String> list1 = getList("/Users/swapnil/IdeaProjects/MovieList/src/imdb.txt");
          ArrayList<String> list2 = getList("/Users/swapnil/IdeaProjects/MovieList/src/sight_and_sound.txt");
          ArrayList<String> list3 = getList("/Users/swapnil/IdeaProjects/MovieList/src/3_lists.txt");

          //Sort lists
          Collections.sort(list1);
          Collections.sort(list2);
          Collections.sort(list3);

          System.out.println("My test" + SetAndMaps.groupByNumChars(list3));

          System.out.println("***\nintersection\n***");
          System.out.println(SetAndMaps.intersection(list1, list2));

          System.out.println("***\nfrequent\n***");
          System.out.println(SetAndMaps.frequent(list3, 3));

          System.out.println("***\ngroupByNumChars\n***");
          System.out.println(SetAndMaps.groupByNumChars(list2));
      }
  }
  ------------------------------------------------------------------------------------------------------------------------------------------------------------------
  import java.util.*;

  public class SetAndMaps {

      // Prints all movies present in the both the files/ lists
      public static String intersection(List<String> list1, List<String> list2) {
          Set<String> movieList1 = new HashSet<>(list1);
          Set<String> movieList2 = new HashSet<>(list2);
          Set<String> intersection = new HashSet<>();

          if(movieList1.size() < movieList2.size() ){
              intersection = movieList2;
              intersection.retainAll(movieList1);
          }else{
              intersection = movieList1;
              intersection.retainAll(movieList2);
          }

          ArrayList<String> matchingVals = new ArrayList<>();
          for (String element : intersection) {
              matchingVals.add(element);
          }
          Collections.sort(matchingVals); //nlogn
          String result = "";
          for (String element : matchingVals) {
              result = result + element;
              result = result + "\n";
          }
          return result;
      }

      // method to prints all movies that occur frequent
      public static String frequent(List<String> list, int k) {
          Map<String, Integer> movieTMap = new TreeMap<String, Integer>();
          for (String element : list) {
              Integer num = movieTMap.get(element);
              if (num == null) movieTMap.put(element, 1);
              else movieTMap.put(element, num + 1);
          }
          String result = "";
          for (Map.Entry<String, Integer> entry : movieTMap.entrySet()) {
              if (entry.getValue() >= k) {
                  result = result + entry.getKey() + "(" + entry.getValue() + ")";
                  result = result + "\n";
              }
          }
          return result;
      }

      //method to print the movies grouped by number of characters.
      public static String groupByNumChars(List<String> list) {

          Map<Integer, List<String>> movieMap = new TreeMap<Integer, List<String>>();
          for (String element : list) {
              int count = 0;
              for (int i = 0; i < element.length(); i++) {
                  count++;
              }

              List<String> movieNames = movieMap.get(count);
              if (movieNames == null) {
                  movieNames = new ArrayList<String>();
                  movieNames.add(element);
                  movieMap.put(count, movieNames);
              }
              else {
                  if (!movieNames.contains(element)) movieNames.add(element);
              }
          }
          String result = "";
          for (Map.Entry<Integer, List<String>> entry : movieMap.entrySet()) {
              ArrayList<String> temp = (ArrayList<String>) entry.getValue();
              Collections.sort(temp);
              result = result + temp + "\n";
          }
          return result;

      }

  }

  
  ------------------------------------------------------------------------------------------------------------------------------------------------------------------

  Program Output :