diff --git a/src/AccountManager.java b/src/AccountManager.java
new file mode 100644
index 0000000..0c2d8c7
--- /dev/null
+++ b/src/AccountManager.java
@@ -0,0 +1,53 @@
+import java.util.HashMap;
+import java.util.Map;
+
+
+/**
+ * 负责账号验证与学段映射.
+ */
+public final class AccountManager {
+
+
+  private final Map<String, String> userToPassword = new HashMap<>();
+  private final Map<String, String> userToLevel = new HashMap<>();
+
+  /**
+   * 用户姓名密码信息初始化.
+   */
+  public AccountManager() {
+
+    register("张三1", "123", "小学");
+    register("张三2", "123", "小学");
+    register("张三3", "123", "小学");
+
+    register("李四1", "123", "初中");
+    register("李四2", "123", "初中");
+    register("李四3", "123", "初中");
+
+    register("王五1", "123", "高中");
+    register("王五2", "123", "高中");
+    register("王五3", "123", "高中");
+  }
+
+
+  private void register(String user, String pwd, String level) {
+    userToPassword.put(user, pwd);
+    userToLevel.put(user, level);
+  }
+
+  /**
+   * 账号密码匹配.
+   */
+  public boolean validate(String user, String pwd) {
+    return user != null && pwd != null && pwd.equals(userToPassword.get(user));
+  }
+
+  /**
+   * 获取用户初始等级.
+   */
+  public String getLevel(String user) {
+    return userToLevel.get(user);
+  }
+
+
+}
\ No newline at end of file
diff --git a/src/BaseQuestionGenerator.java b/src/BaseQuestionGenerator.java
new file mode 100644
index 0000000..a85191e
--- /dev/null
+++ b/src/BaseQuestionGenerator.java
@@ -0,0 +1,79 @@
+import java.util.ArrayList;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Random;
+import java.util.Set;
+
+/**
+ * 抽象题目生成器基类. 子类需要实现 {@link #generateQuestion()} 来提供不同学段的题目生成逻辑.
+ */
+public abstract class BaseQuestionGenerator {
+
+  /**
+   * 用于生成随机数的随机数生成器.
+   */
+  protected final Random random = new Random();
+
+  /**
+   * 生成一组不重复的数学题目列表.
+   *
+   * @param count             要生成的题目数量.
+   * @param existingQuestions 已经存在的题目集合.
+   * @return 生成的题目列表.
+   */
+  public List<String> generate(int count, Set<String> existingQuestions) {
+    List<String> result = new ArrayList<>();
+    Set<String> seen = new HashSet<>(existingQuestions == null ? 0 : existingQuestions.size());
+    if (existingQuestions != null) {
+      seen.addAll(existingQuestions);
+    }
+
+    int attempts = 0;
+    while (result.size() < count && attempts < count * 20) {
+      String question = generateQuestion();
+      if (!seen.contains(question)) {
+        result.add(question);
+        seen.add(question);
+      }
+      attempts++;
+    }
+
+    return result;
+  }
+
+  /**
+   * 生成一个指定范围内的随机整数.
+   *
+   * @param a 下界.
+   * @param b 上界.
+   * @return 返回一个位于 a 和 b 之间的随机整数.
+   */
+  protected int randInt(int a, int b) {
+    return a + random.nextInt(b - a + 1);
+  }
+
+  /**
+   * 随机返回一个基础运算符: "+", "-", "*", 或 "/".
+   *
+   * @return 随机运算符字符串.
+   */
+  protected String randomBasicOperator() {
+    return switch (random.nextInt(4)) {
+      case 0 -> "+";
+      case 1 -> "-";
+      case 2 -> "*";
+      default -> "/";
+    };
+  }
+
+  /**
+   * 生成单个题目. 子类必须实现该方法以提供不同学段的题目生成逻辑.
+   *
+   * @return 返回生成的数学题目字符串.
+   */
+  protected abstract String generateQuestion();
+}
+
+
+
+
diff --git a/src/Constants.java b/src/Constants.java
new file mode 100644
index 0000000..1f297f7
--- /dev/null
+++ b/src/Constants.java
@@ -0,0 +1,16 @@
+
+/** 常量定义. */
+public final class Constants {
+  public static final String BASE_OUTPUT_DIR = "output"; // 主输出文件夹
+  public static final int MIN_QUESTIONS = 10;
+  public static final int MAX_QUESTIONS = 30;
+  public static final int MIN_OPERANDS = 1;
+  public static final int MAX_OPERANDS = 5;
+  public static final int MIN_VALUE = 1;
+  public static final int MAX_VALUE = 100;
+
+
+  private Constants() {
+  // no instances
+  }
+}
\ No newline at end of file
diff --git a/src/FileManager.java b/src/FileManager.java
new file mode 100644
index 0000000..b466569
--- /dev/null
+++ b/src/FileManager.java
@@ -0,0 +1,99 @@
+import java.io.BufferedWriter;
+import java.io.IOException;
+import java.nio.charset.StandardCharsets;
+import java.nio.file.Files;
+import java.nio.file.Path;
+import java.nio.file.Paths;
+import java.text.SimpleDateFormat;
+import java.util.Date;
+import java.util.HashSet;
+import java.util.List;
+import java.util.Set;
+
+/**
+ * 负责与磁盘文件交互：读取历史题目、保存新生成的试卷文件. 所有生成的卷子会保存在 {@code Constants.BASE_OUTPUT_DIR} 目录下，
+ * 其中按照用户账号创建子目录。每次保存的文件名为 {@code yyyy-MM-dd-HH-mm-ss.txt} 格式.
+ */
+public final class FileManager {
+
+  /**
+   * 试卷保存的根目录路径.
+   */
+  private final Path baseDir;
+
+  /**
+   * 构造方法。初始化输出目录. 如果 {@link Constants#BASE_OUTPUT_DIR} 指定的目录不存在， 则会自动创建.
+   *
+   * @throws RuntimeException 如果目录无法创建时抛出运行时异常.
+   */
+  public FileManager() {
+    this.baseDir = Paths.get(Constants.BASE_OUTPUT_DIR);
+    try {
+      Files.createDirectories(baseDir);
+    } catch (IOException e) {
+      throw new RuntimeException("无法创建输出目录: " + baseDir, e);
+    }
+  }
+
+  /**
+   * 查重功能 读取指定用户历史上已生成的所有题目内容，用于避免重复出题. 该方法会遍历用户目录下所有以 <code>.txt</code> 结尾的文件， 过滤掉形如
+   * "第x题:"的题号前缀，只收集真实题干文本.
+   *
+   * @param username 用户名（用于定位其专属文件夹）
+   * @return 包含用户所有历史题目的字符串集合；如果目录不存在或无文件则返回空集合.
+   */
+  public Set<String> loadExistingQuestions(String username) {
+    Path userDir = baseDir.resolve(username);
+    Set<String> existing = new HashSet<>();
+    if (!Files.exists(userDir)) {
+      return existing;
+    }
+    try {
+      Files.list(userDir)
+          .filter(p -> p.toString().endsWith(".txt"))
+          .forEach(p -> {
+            try {
+              List<String> lines = Files.readAllLines(p, StandardCharsets.UTF_8);
+              for (String line : lines) {
+                String t = line.trim();
+                // 只保留题目正文
+                if (!t.isEmpty() && !t.matches("^第\\d+题.*$")) {
+                  existing.add(t);
+                }
+              }
+            } catch (IOException ignore) {
+              // 忽略单个文件失败
+            }
+          });
+    } catch (IOException ignore) {
+      // 遍历目录失败时忽略
+    }
+    return existing;
+  }
+
+  /**
+   * 将生成的试卷保存到指定用户目录中. 保存路径格式： BASE_OUTPUT_DIR/用户名/yyyy-MM-dd-HH-mm-ss.txt 每道题会以“第n题:
+   * 题目”的形式写入文件，并在题目间留一行空行.
+   *
+   * @param username  当前登录的用户名，用于确定子目录
+   * @param questions 题目列表，每个元素是一道题的字符串
+   * @return 保存的试卷文件的完整 {@link Path}
+   * @throws IOException 当文件写入或目录创建失败时抛出.
+   */
+  public Path saveExam(String username, List<String> questions) throws IOException {
+    Path userDir = baseDir.resolve(username);
+    Files.createDirectories(userDir);
+
+    String name = new SimpleDateFormat("yyyy-MM-dd-HH-mm-ss").format(new Date()) + ".txt";
+    Path out = userDir.resolve(name);
+
+    try (BufferedWriter w = Files.newBufferedWriter(out, StandardCharsets.UTF_8)) {
+      for (int i = 0; i < questions.size(); i++) {
+        w.write(String.format("第%d题: %s", i + 1, questions.get(i)));
+        w.newLine();
+        w.newLine();
+      }
+    }
+    return out;
+  }
+}
diff --git a/src/HighQuestionGenerator.java b/src/HighQuestionGenerator.java
new file mode 100644
index 0000000..004f890
--- /dev/null
+++ b/src/HighQuestionGenerator.java
@@ -0,0 +1,47 @@
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 高中题目生成器.
+ */
+class HighQuestionGenerator extends BaseQuestionGenerator {
+
+  @Override
+  protected String generateQuestion() {
+    int ops = randInt(Constants.MIN_OPERANDS, Constants.MAX_OPERANDS);
+    List<String> tokens = new ArrayList<>();
+    boolean hasTrig = false;
+
+    for (int i = 0; i < ops; i++) {
+      if (!hasTrig && random.nextDouble() < 0.5) {
+        tokens.add(randomTrig());
+        hasTrig = true;
+      } else if (random.nextDouble() < 0.2) {
+        tokens.add("(" + randInt(Constants.MIN_VALUE, Constants.MAX_VALUE) + "^2)");
+      } else {
+        tokens.add(String.valueOf(randInt(Constants.MIN_VALUE, Constants.MAX_VALUE)));
+      }
+      if (i < ops - 1) {
+        tokens.add(randomBasicOperator());
+      }
+    }
+
+    if (!hasTrig) {
+      int pos = Math.max(0, random.nextInt(tokens.size() / 2 + 1) * 2);
+      tokens.add(pos, randomTrig());
+      if (pos + 1 < tokens.size()) {
+        tokens.add(pos + 1, "+");
+      }
+    }
+
+    return String.join(" ", tokens);
+  }
+
+  private String randomTrig() {
+    return switch (random.nextInt(3)) {
+      case 0 -> "sin(" + randInt(0, 90) + ")";
+      case 1 -> "cos(" + randInt(0, 90) + ")";
+      default -> "tan(" + randInt(0, 60) + ")";
+    };
+  }
+}
diff --git a/src/MathExamGenerator.java b/src/MathExamGenerator.java
new file mode 100644
index 0000000..f38714c
--- /dev/null
+++ b/src/MathExamGenerator.java
@@ -0,0 +1,155 @@
+import java.io.IOException;
+import java.nio.file.Path;
+import java.util.List;
+import java.util.Scanner;
+import java.util.Set;
+
+/**
+ * 程序入口类，提供命令行交互以生成中小学数学卷子.
+ */
+public final class MathExamGenerator {
+
+  private final AccountManager accountManager = new AccountManager();
+  private final FileManager fileManager = new FileManager();
+
+  /**
+   * 程序主入口.
+   *
+   * @param unused 未使用的命令行参数
+   */
+  public static void main(String[] unused) {
+    new MathExamGenerator().run();
+  }
+
+  /**
+   * 运行程序的主循环，包含登录、题目生成、文件保存等逻辑.
+   */
+  private void run() {
+    try (Scanner scanner = new Scanner(System.in)) {
+      while (true) {
+        String currentUser = login(scanner);
+        String currentLevel = accountManager.getLevel(currentUser);
+
+        while (true) {
+          System.out.printf(
+              "准备生成 %s 数学题目，请输入生成题目数量（输入-1将退出当前用户，重新登录）：",
+              currentLevel);
+          String line = scanner.nextLine().trim();
+
+          if ("-1".equals(line)) {
+            break;
+          }
+
+          if (line.startsWith("切换为")) {
+            currentLevel = handleLevelSwitch(line, currentLevel);
+            continue;
+          }
+
+          handleQuestionGeneration(currentUser, currentLevel, line);
+        }
+      }
+    }
+  }
+
+  /**
+   * 登录流程：验证用户名和密码.
+   *
+   * @param scanner 控制台输入流.
+   * @return 成功登录的用户名.
+   */
+  private String login(Scanner scanner) {
+    while (true) {
+      System.out.print("请输入用户名 密码（用空格分隔）：");
+      String line = scanner.nextLine().trim();
+      if (line.isEmpty()) {
+        continue;
+      }
+
+      String[] parts = line.split("\\s+");
+      if (parts.length < 2) {
+        System.out.println("请输入正确的用户名、密码");
+        continue;
+      }
+
+      if (accountManager.validate(parts[0], parts[1])) {
+        String username = parts[0];
+        System.out.println("当前选择为 " + accountManager.getLevel(username) + " 出题");
+        return username;
+      } else {
+        System.out.println("用户名或密码错误，请重新输入");
+      }
+    }
+  }
+
+  /**
+   * 处理学段切换命令.
+   *
+   * @param line         用户输入
+   * @param currentLevel 当前学段
+   * @return 切换后的学段（若输入无效则返回原学段）
+   */
+  private String handleLevelSwitch(String line, String currentLevel) {
+    String opt = line.replaceFirst("切换为", "").trim();
+    if (!"小学".equals(opt) && !"初中".equals(opt) && !"高中".equals(opt)) {
+      System.out.println("请输入小学、初中或高中三个选项中的一个");
+      return currentLevel;
+    }
+    System.out.println("当前选择为 " + opt + " 出题");
+    return opt;
+  }
+
+  /**
+   * 生成指定数量的题目并保存为试卷文件.
+   *
+   * @param username 用户名
+   * @param level    学段
+   * @param line     用户输入的题目数量
+   */
+  private void handleQuestionGeneration(String username, String level, String line) {
+    int num;
+    try {
+      num = Integer.parseInt(line);
+    } catch (NumberFormatException e) {
+      System.out.println("请输入有效的整数数量或-1退出");
+      return;
+    }
+
+    if (num < Constants.MIN_QUESTIONS || num > Constants.MAX_QUESTIONS) {
+      System.out.printf(
+          "题目数量的有效输入范围是 %d-%d（含）%n", Constants.MIN_QUESTIONS, Constants.MAX_QUESTIONS);
+      return;
+    }
+
+    BaseQuestionGenerator generator = getGenerator(level);
+    Set<String> existing = fileManager.loadExistingQuestions(username);
+    List<String> questions = generator.generate(num, existing);
+
+    if (questions.size() < num) {
+      System.out.println("无法生成足够不重复的题目，请删除部分历史题目或减少生成数量");
+      return;
+    }
+
+    try {
+      Path path = fileManager.saveExam(username, questions);
+      // 转为 String 打印相对路径
+      System.out.println("试卷已保存：" + path);
+    } catch (IOException e) {
+      System.out.println("保存文件时出错：" + e.getMessage());
+    }
+  }
+
+  /**
+   * 根据学段返回对应的题目生成器.
+   *
+   * @param level 学段
+   * @return 对应的 BaseQuestionGenerator 实例
+   */
+  private BaseQuestionGenerator getGenerator(String level) {
+    return switch (level) {
+      case "小学" -> new PrimaryQuestionGenerator();
+      case "初中" -> new MiddleQuestionGenerator();
+      case "高中" -> new HighQuestionGenerator();
+      default -> new PrimaryQuestionGenerator();
+    };
+  }
+}
diff --git a/src/MiddleQuestionGenerator.java b/src/MiddleQuestionGenerator.java
new file mode 100644
index 0000000..57c81c4
--- /dev/null
+++ b/src/MiddleQuestionGenerator.java
@@ -0,0 +1,41 @@
+import java.util.ArrayList;
+import java.util.List;
+
+/**
+ * 初中题目生成器.
+ */
+class MiddleQuestionGenerator extends BaseQuestionGenerator {
+
+  @Override
+  protected String generateQuestion() {
+    int ops = randInt(Constants.MIN_OPERANDS, Constants.MAX_OPERANDS);
+    List<String> tokens = new ArrayList<>();
+    boolean hasPowerOrSqrt = false;
+
+    for (int i = 0; i < ops; i++) {
+      if (!hasPowerOrSqrt && random.nextDouble() < 0.4) {
+        if (random.nextBoolean()) {
+          tokens.add("(" + randInt(Constants.MIN_VALUE, Constants.MAX_VALUE) + "^2)");
+        } else {
+          tokens.add("sqrt(" + randInt(Constants.MIN_VALUE, Constants.MAX_VALUE) + ")");
+        }
+        hasPowerOrSqrt = true;
+      } else {
+        tokens.add(String.valueOf(randInt(Constants.MIN_VALUE, Constants.MAX_VALUE)));
+      }
+      if (i < ops - 1) {
+        tokens.add(randomBasicOperator());
+      }
+    }
+
+    if (!hasPowerOrSqrt) {
+      int pos = Math.max(0, random.nextInt(tokens.size() / 2 + 1) * 2);
+      tokens.add(pos, "sqrt(4)");
+      if (pos + 1 < tokens.size()) {
+        tokens.add(pos + 1, "+");
+      }
+    }
+
+    return String.join(" ", tokens);
+  }
+}
\ No newline at end of file
diff --git a/src/PrimaryQuestionGenerator.java b/src/PrimaryQuestionGenerator.java
new file mode 100644
index 0000000..b5e21e5
--- /dev/null
+++ b/src/PrimaryQuestionGenerator.java
@@ -0,0 +1,94 @@
+import java.util.ArrayList;
+import java.util.List;
+
+class PrimaryQuestionGenerator extends BaseQuestionGenerator {
+
+  @Override
+  protected String generateQuestion() {
+    List<String> numbers = generateNumbers();
+    List<String> operators = generateOperators(numbers);
+    List<String> tokens = combineTokens(numbers, operators);
+    addRandomBrackets(tokens);
+    return String.join(" ", tokens);
+  }
+
+  /**
+   * 生成操作数列表.
+   */
+  private List<String> generateNumbers() {
+    int ops = randInt(2, Constants.MAX_OPERANDS);
+    List<String> numbers = new ArrayList<>();
+    for (int i = 0; i < ops; i++) {
+      numbers.add(String.valueOf(randInt(1, Constants.MAX_VALUE)));
+    }
+    return numbers;
+  }
+
+  /**
+   * 生成操作符列表，保证减法不产生负数.
+   */
+  private List<String> generateOperators(List<String> numbers) {
+    List<String> operators = new ArrayList<>();
+    String current = numbers.getFirst();
+    for (int i = 1; i < numbers.size(); i++) {
+      String op = randomBasicOperator();
+      if ("-".equals(op)) {
+        int left = Integer.parseInt(current.replaceAll("[^0-9]", ""));
+        int right = Integer.parseInt(numbers.get(i));
+        if (left < right) {
+          op = random.nextBoolean() ? "+" : "*";
+        }
+      }
+      operators.add(op);
+      current = computeIntermediate(current, numbers.get(i), op);
+    }
+    return operators;
+  }
+
+  /**
+   * 合成数字和运算符为 tokens 列表.
+   */
+  private List<String> combineTokens(List<String> numbers, List<String> operators) {
+    List<String> tokens = new ArrayList<>();
+    tokens.add(numbers.getFirst());
+    for (int i = 1; i < numbers.size(); i++) {
+      tokens.add(operators.get(i - 1));
+      tokens.add(numbers.get(i));
+    }
+    return tokens;
+  }
+
+  /**
+   * 随机为子表达式添加一对括号，不包裹整个表达式.
+   */
+  private void addRandomBrackets(List<String> tokens) {
+    int ops = (tokens.size() + 1) / 2;
+    if (ops < 2 || !random.nextBoolean()) {
+      return;
+    }
+
+    int pairCount = ops - 1;
+    int chosenOpIndex = random.nextInt(pairCount);
+    int leftIndex = chosenOpIndex * 2;
+    int rightIndex = chosenOpIndex * 2 + 2;
+
+    if (!(leftIndex == 0 && rightIndex == tokens.size() - 1)) {
+      tokens.add(leftIndex, "(");
+      tokens.add(rightIndex + 2, ")");
+    }
+  }
+
+  /**
+   * 计算当前中间值，用于保证减法不产生负数.
+   */
+  private String computeIntermediate(String current, String next, String op) {
+    int c = Integer.parseInt(current);
+    int n = Integer.parseInt(next);
+    return switch (op) {
+      case "*" -> String.valueOf(c * n);
+      case "+" -> String.valueOf(c + n);
+      case "/" -> n != 0 ? String.valueOf(c / n) : String.valueOf(c);
+      default -> String.valueOf(c); // 避免减法导致负数
+    };
+  }
+}