限制题目数量

src/service/QuestionService.java

@@ -6,10 +6,14 @@ import java.util.*;
 public class QuestionService {
   /*生成试卷的题目部分*/
   public List<Question> generateQuestions(String difficulty, int count) {
+    if(count < 10 || count > 30) {
+      return null;
+    }
+    
     List<Question> questions = new ArrayList<>();
     Set<String> usedQuestions = new HashSet<>();
     QuestionGenerator generator = QuestionGeneratorFactory.getGenerator(difficulty);
-        
+    
     while (questions.size() < count) {
       Question q = generator.generateQuestion();
       if (usedQuestions.add(q.getContent())) {