Hashmap

import java.util.Collections;
import java.util.HashMap;
import java.util.HashSet;
import java.util.Map;
import java.util.Set;
 
public class Interest {
    public static Map<String, Double> calculateRatesByInterest(Map<String, Map<String, Double>> rateByInterestBySite,
                                                               Map<String, Integer> visitsBySite) {
        Set<String> interests = new HashSet<String>();
        for (Map<String, Double> rateByInterest : rateByInterestBySite.values()) {
            interests.addAll(rateByInterest.keySet());
        }
 
        Map<String, Double> rateByInterest = new HashMap<String, Double>();
        for (Map.Entry<String, Integer> entry : visitsBySite.entrySet()) {
            for (String interest : interests) {
                String site = entry.getKey();
                Integer visits = entry.getValue();
                Map<String, Double> rateByInterestForSite = rateByInterestBySite.get(site);
                if (rateByInterestForSite != null) {
                    Double rateOfInterest = rateByInterestForSite.get(interest);
                    if (rateOfInterest != null) {
                        Double rate = rateByInterest.get(interest);
                        if (rate == null) {
                            rate = 0.0;
                        }
                        rateByInterest.put(interest, rate + (visits * rateOfInterest));
 
                    }
                }
            }
        }
 
        Double maxRate = Collections.max(rateByInterest.values());
        Map<String, Double> normalizedRateByInterest = new HashMap<String, Double>();
        for (Map.Entry<String, Double> entry : rateByInterest.entrySet()) {
            String interest = entry.getKey();
            Double rate = entry.getValue();
            normalizedRateByInterest.put(interest, rate / maxRate);
        }
 
        return normalizedRateByInterest;
    }
 
    public static void main(String[] args) {
        Map<String, Map<String, Double>> rateByInterestBySite = new HashMap<String, Map<String, Double>>();
        Map<String, Double> yandexInterests = new HashMap<String, Double>();
        Map<String, Double> fishkiInterests = new HashMap<String, Double>();
 
        yandexInterests.put("searcher", 1.0);
        yandexInterests.put("fun", 0.4);
 
        fishkiInterests.put("fun", 1.0);
 
        rateByInterestBySite.put("yandex", yandexInterests);
        rateByInterestBySite.put("fishki", fishkiInterests);
 
        Map<String, Integer> visits = new HashMap<String, Integer>();
        visits.put("yandex", 3);
        visits.put("fishki", 1);
 
        Map<String, Double> result = calculateRatesByInterest(rateByInterestBySite, visits);
        System.out.println(result.get("fun"));
    }
}