code: public List<CandidateAnswer> getTopNCandidateAnswer(int topN) {
          List<CandidateAnswer> topNcandidateAnswers = new ArrayList<>();
          List<CandidateAnswer> allCandidateAnswers = getAllCandidateAnswer();
          if (topN > allCandidateAnswers.size()) {
              topN = allCandidateAnswers.size();
          }
          for (int i = 0; i < topN; i++) {
              topNcandidateAnswers.add(allCandidateAnswers.get(i));
          }
          return topNcandidateAnswers;
      }
docs: 获取topN候选答案
  
  @param topN
  @return topN候选答案