Solution: The Fraud Detection Ring

import java.io.IOException;
import java.nio.file.Files;
import java.nio.file.Path;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
import java.util.List;
public class SecurityScanner {
    public static Map<Integer, Set<String>> loadUserDevices(String filePath) {
        Map<Integer, Set<String>> userMap = new HashMap<>();
        try {
            List<String> lines = Files.readAllLines(Path.of(filePath));
            
            // Start at 1 to skip header
            for (int i = 1; i < lines.size(); i++) {
                String[] parts = lines.get(i).split(",");
                // Parse CSV columns
                int userId = Integer.parseInt(parts[0].trim());
                String device = parts[1].trim();
                
                // Ensure the Set exists for this user
                userMap.putIfAbsent(userId, new HashSet<>());
                
                // Add the device (Set handles uniqueness automatically)
                userMap.get(userId).add(device);
            }
        } catch (IOException e) {
            System.out.println("Error reading file: " + e.getMessage());
        }
        return userMap;
    }
    public static Set<Integer> identifySuspiciousUsers(Map<Integer, Set<String>> userDeviceMap, int limit) {
        Set<Integer> suspiciousUsers = new HashSet<>();
        
        for (Map.Entry<Integer, Set<String>> entry : userDeviceMap.entrySet()) {
            Integer userId = entry.getKey();
            Set<String> devices = entry.getValue();
            
            // Check if unique device count exceeds the limit
            if (devices.size() > limit) {
                suspiciousUsers.add(userId);
            }
        }
        
        return suspiciousUsers;
    }
    public static void main(String[] args) {
        System.out.println("Scanning logs...");
        Map<Integer, Set<String>> data = loadUserDevices("log.csv");
        
        System.out.println("Total Users Found: " + data.size());
        System.out.println("--- Device Counts ---");
        for (Integer user : data.keySet()) {
            System.out.println(" - User " + user + ": " + data.get(user).size() + " unique devices");
        }
        System.out.println("\n--- DETECTING THREATS (Limit: 3) ---");
        Set<Integer> flagged = identifySuspiciousUsers(data, 3);
        
        if (flagged.isEmpty()) {
            System.out.println("No suspicious activity detected.");
        } else {
            System.out.println("Flagged Users: " + flagged);
        }
    }
}