import java.util.*; public class VotingSystem { private Map candidates; // Stores candidate_id as key and votes as value private Map voters; // Tracks each voter's voting history public VotingSystem() { this.candidates = new HashMap<>(); // Initialize candidates map this.voters = new HashMap<>(); // Initialize voters map } public boolean registerCandidate(String candidateId) { if (candidates.containsKey(candidateId)) { return false; // Candidate is already registered } candidates.put(candidateId, 0); // Initialize candidates with 0 votes return true; } public boolean vote(long timestamp, String voterId, String candidateId) { if (!candidates.containsKey(candidateId)) { return false; // Return false if candidate is not registered } VotingHistory voterHistory = voters.computeIfAbsent(voterId, k -> new VotingHistory()); voterHistory.getVotes().add(candidateId); // Record the vote voterHistory.getTimestamps().add(timestamp); // Record the time of the vote candidates.put(candidateId, candidates.get(candidateId) + 1); // Increment vote count for the candidate return true; } public Integer getVotes(String candidateId) { return candidates.get(candidateId); // Retrieve vote count for a candidate or null if not found } public List topNCandidates(int n) { return candidates.entrySet().stream() .sorted((entry1, entry2) -> entry2.getValue().compareTo(entry1.getValue())) .limit(n) .map(Map.Entry::getKey) .toList(); // Return top n candidates based on votes } private static class VotingHistory { private final List votes; private final List timestamps; public VotingHistory() { this.votes = new ArrayList<>(); this.timestamps = new ArrayList<>(); } public List getVotes() { return votes; } public List getTimestamps() { return timestamps; } } }