private PostingsList getTfidfQuery(Query query) {

        /** Build query vector */
        ArrayList<Double> q = new ArrayList<>();

        HashMap<String, Integer> tkns = new HashMap<>();
        for (int i = 0; i < query.queryterm.size(); i++) {
            if (!tkns.containsKey(query.queryterm.get(i).term))
                q.add(query.queryterm.get(i).weight);
            else {
                int idx = tkns.get(query.queryterm.get(i).term);
                q.set(idx, q.get(idx) + query.queryterm.get(i).weight);
            }
        }

        ArrayList<TokenIndexData> postingsLists = getPostingsLists(query);
        HashMap<Integer, PostingsEntry> scores = new HashMap<>();
        HashMap<Integer, Double> denom = new HashMap<>();

        int i = 0;
        for (TokenIndexData pt: postingsLists) {
            PostingsList pl = pt.postingsList;

            for (PostingsEntry pe: pl) {

                double tfidf = tfidf(pe, pl);

                double score = q.get(i) * tfidf;

                if (!scores.containsKey(pe.docID)) {
                    scores.put(pe.docID, new PostingsEntry(pe.docID, score));
                }
                else {
                    scores.get(pe.docID).score += score;
                }
            }
            i++;
        }

        PostingsList results = new PostingsList();

        /** Normalize score */
        for (int docID: scores.keySet()) {
            PostingsEntry pe = scores.get(docID);

            pe.score /= Index.docLengths.get(pe.docID);

            results.add(pe);
        }

        Collections.sort(results);

        return results;
    }

    private double tfidf(PostingsEntry pe, PostingsList pl) {
        double tf = pe.getOccurences();
        double idf = Math.log(Index.docNames.size() / pl.size());

        double tfidf = tf * idf;
        return tfidf;
    }