import java.util.ArrayList; import java.util.HashMap; import java.util.List; import java.util.Map; import java.util.Scanner;

/**

• The Tallyer class provides functionality for reading ID and topic pairs from user input,

• and tallying the number of occurrences of each topic. */ public class Tallyer {

  /**

  • The main method serves as the entry point for the program. It reads pairs of IDs and topics

  • from standard input, stores them in lists, and then calculates the number of occurrences

  • of each topic. The IDs and topics are guaranteed to not include internal whitespace.

  • @param args command-line arguments (not used in this implementation) */ public static void main(String[] args) { Scanner input = new Scanner(System.in);

    List ids = new ArrayList<>(); List topics = new ArrayList<>();

    // Reading input for IDs and topics // Assumes input is well formed into pairs while (input.hasNext()) { ids.add(input.next()); topics.add(input.next()); } input.close();

    // Wave 1 Map<String, Integer> topicCounts = tallyTopics(topics); System.out.println("Here are how many times each topic appears (unfiltered):"); System.out.println(topicCounts);

    // Wave 2 Map<String, Integer> topicCountsFiltered = tallyTopicsFiltered(ids, topics); System.out.println("Here are how many times each topic appears (filtered):"); System.out.println(topicCountsFiltered); }

  /**

  • Tally the occurrences of each topic from the provided lists of topics.

  • This method takes a list of topics and returns a map where each topic is associated

  • with the number of times it appears in the input.

  • @param topics a list of strings representing the topics to be tallied

  • @return a map containing topics as keys and their occurrence counts as values */ public static Map<String, Integer> tallyTopics(List topics) { // Create a map to hold the count of each topic Map<String, Integer> topicCountMap = new HashMap<>();

    // Iterate through the list of topics and count occurrences for (String topic : topics) { topicCountMap.put(topic, topicCountMap.getOrDefault(topic, 0) + 1); }

    System.out.println("Topic counts: " + topicCountMap); // Debugging line return topicCountMap; // Return the map with topic counts }

  /**

  • Tally the occurrences of each topic from the provided lists of IDs and topics.

  • This method takes two lists, one of IDs and one of topics, and returns a map

  • where each topic is associated with the number of times it appears in the input.

  • However, any user who did not enter exactly 2 topics should not have their votes counted.

  • @param ids a list of strings representing IDs associated with each topic

  • @param topics a list of strings representing the topics to be tallied

  • @return a map containing topics as keys and their occurrence counts as values */ public static Map<String, Integer> tallyTopicsFiltered(List ids, List topics) { Map<String, Integer> filteredTopicCountMap = new HashMap<>();

    // Create a map to count the occurrences of IDs Map<String, Integer> idCountMap = new HashMap<>(); for (String id : ids) { idCountMap.put(id, idCountMap.getOrDefault(id, 0) + 1); }

    System.out.println("ID counts: " + idCountMap); // Debugging line

    // Iterate through the topics and count occurrences for valid IDs for (int i = 0; i < ids.size(); i++) { String id = ids.get(i); String topic = topics.get(i); // Only count if the ID appears exactly twice if (idCountMap.get(id) == 2) { filteredTopicCountMap.put(topic, filteredTopicCountMap.getOrDefault(topic, 0) + 1); } }

    System.out.println("Filtered topic counts: " + filteredTopicCountMap); // Debugging line return filteredTopicCountMap; // Return the map with filtered topic counts } }