public static class ACReducer extends Reducer<Text,Text,Text,Text> {

        // I used a hashmap which will store category as key, and a list of string where each elements will contain: the actual term, value 'A', and value 'C'
        // First we need to make a pair of the category with each word in it. (the hashmap guarantees that we have the distinct words)
        @Override
        protected void reduce(Text key, Iterable<Text> values, Context context) throws IOException, InterruptedException {
            String categoryKey = key.toString();
            HashSet<String> docLister = new HashSet<>();
			 // This HashMap counts the number of documents in the category with the term (A). The term is defined in the key.
			HashMap<String, Long> numOfDocsWithTermT = new HashMap<String, Long>();
            for (Text val : values) {
				String currentTerm = uTerm.toString().split("\\s")[1];
				numOfDocsWithTermT.computeIfAbsent(currentTerm, k -> (long) 0);
				long numOfDocs = numOfDocsWithTermT.get(currentTerm);
                numOfDocs++;
                numOfDocsWithTermT.put(currentTerm, numOfDocs);
                uniqueTermDocPairs.add(new Text(val.toString()));
                docLister.add(val.toString().split("\\s")[0]);
            }



            // Calculate values A and C
            long totalNumOfDocsInCat =  docLister.size();

            numOfDocsWithTermT.entrySet().stream().forEach(term ->
                    {
                        String termAC = term.getKey().toString() + " " +
                                term.getValue() + " " +
                                (totalNumOfDocsInCat - term.getValue());

                        try {
                            context.write(new Text(categoryKey), new Text(termAC));
                        } catch (IOException e) {
                            e.printStackTrace();
                        } catch (InterruptedException e) {
                            e.printStackTrace();
                        }
                    }
            );
        }
    }