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

// 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);
  }
}