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src/main/java/com/example/myapp/service/ExamService.java

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+// ExamService.java
+package com.example.myapp.service;
+
+import com.example.myapp.model.Exam;
+import com.example.myapp.model.Question;
+import java.util.List;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.Map;
+
+public class ExamService {
+  private Map<String, Exam> userExams = new ConcurrentHashMap<>();
+  private static final ExamService instance = new ExamService();
+
+  public static ExamService getInstance() {
+    return instance;
+  }
+
+  public boolean generateExam(String gradeLevel, int questionCount, String email) {
+    try {
+      List<Question> questions = MathQuestionGenerator.generateQuestions(gradeLevel, questionCount);
+      Exam exam = new Exam(gradeLevel, questionCount, questions);
+      userExams.put(email, exam);
+      return true;
+    } catch (Exception e) {
+      e.printStackTrace();
+      return false;
+    }
+  }
+
+  public Exam getCurrentExam(String email) {
+    return userExams.get(email);
+  }
+
+  public boolean submitAnswer(String email, int questionIndex, String selectedAnswer) {
+    Exam exam = userExams.get(email);
+    if (exam != null && questionIndex >= 0 && questionIndex < exam.getQuestions().size()) {
+      exam.getQuestions().get(questionIndex).setUserAnswer(selectedAnswer);
+      return true;
+    }
+    return false;
+  }
+
+  // 在 ExamService.java 的 calculateScore 方法中修改答案比较逻辑
+  public int calculateScore(String email) {
+    Exam exam = userExams.get(email);
+    if (exam == null) return 0;
+
+    int correctCount = 0;
+    for (Question question : exam.getQuestions()) {
+      String userAnswer = question.getUserAnswer();
+      String correctAnswer = question.getCorrectAnswer();
+
+      // 使用容差比较答案（针对小数）
+      if (isAnswerCorrect(userAnswer, correctAnswer)) {
+        correctCount++;
+      }
+    }
+
+    int score = (int) ((correctCount * 100.0) / exam.getQuestions().size());
+    exam.setScore(score);
+    return score;
+  }
+
+  // 新增答案比较方法，支持小数容差
+  private boolean isAnswerCorrect(String userAnswer, String correctAnswer) {
+    if (userAnswer == null || correctAnswer == null) {
+      return false;
+    }
+
+    try {
+      // 去除选项标签（如"A. "）
+      String cleanUserAnswer = userAnswer.replaceAll("^[A-D]\\.\\s*", "");
+      String cleanCorrectAnswer = correctAnswer.replaceAll("^[A-D]\\.\\s*", "");
+
+      // 尝试解析为数字进行比较
+      double userValue = Double.parseDouble(cleanUserAnswer);
+      double correctValue = Double.parseDouble(cleanCorrectAnswer);
+
+      // 使用容差比较
+      return Math.abs(userValue - correctValue) < 0.01;
+    } catch (NumberFormatException e) {
+      // 如果无法解析为数字，进行字符串比较
+      return userAnswer.trim().equals(correctAnswer.trim());
+    }
+  }
+
+  public void clearExam(String email) {
+    userExams.remove(email);
+  }
+}