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diff --git a/src/MathPaperGenerator.java b/src/MathPaperGenerator.java
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-import java.io.*;
-import java.nio.charset.StandardCharsets;
-import java.nio.file.*;
-import java.text.SimpleDateFormat;
-import java.util.*;
-import java.util.stream.Collectors;
-
-/**
- * MathPaperGenerator
- * 实现 PDF 要求的命令行程序（登录、出题、切换难度、去重、保存）。
- *
- * 使用：javac MathPaperGenerator.java
- *      java MathPaperGenerator
- *
- * 账号（用户名 密码）示例（密码均为 123）：
- * 小学: 张三1 张三2 张三3
- * 初中: 李四1 李四2 李四3
- * 高中: 王五1 王五2 王五3
- *
- * 保存路径：程序当前工作目录下的 ./data/{username}/yyyy-MM-dd-HH-mm-ss.txt
- */
-public class MathPaperGenerator {
-    // 账号信息
-    static class Account {
-        String username;//用户名
-        String password;//密码
-        Level level;//出题等级
-        Account(String u, String p, Level l) { 
-            username = u; 
-            password = p; 
-            level = l; 
-        }
-    }
-    enum Level { PRIMARY, MIDDLE, HIGH }
-
-    private static final Map<String, Account> accounts = new HashMap<>();
-    private static final Scanner scanner = new Scanner(System.in, StandardCharsets.UTF_8.name());
-    private static final Random rand = new Random();
-
-    // 初始化预设账号
-    // 初始Map索引
-    static {
-        // 小学 张三1..3
-        accounts.put("张三1", new Account("张三1","123", Level.PRIMARY));
-        accounts.put("张三2", new Account("张三2","123", Level.PRIMARY));
-        accounts.put("张三3", new Account("张三3","123", Level.PRIMARY));
-        // 初中 李四1..3
-        accounts.put("李四1", new Account("李四1","123", Level.MIDDLE));
-        accounts.put("李四2", new Account("李四2","123", Level.MIDDLE));
-        accounts.put("李四3", new Account("李四3","123", Level.MIDDLE));
-        // 高中 王五1..3
-        accounts.put("王五1", new Account("王五1","123", Level.HIGH));
-        accounts.put("王五2", new Account("王五2","123", Level.HIGH));
-        accounts.put("王五3", new Account("王五3","123", Level.HIGH));
-    }
-
-    public static void main(String[] args) {
-        System.out.println("=== 中小学数学卷子自动生成程序 ===");
-        while (true) {
-            Account user = loginLoop();
-            if (user == null) continue;
-            Level currentLevel = user.level;
-            System.out.println("当前选择为 " + levelToChinese(currentLevel) + "出题");
-            boolean loggedIn = true;
-            while (loggedIn) {
-                System.out.print("系统提示“准备生成 " + levelToChinese(currentLevel) + "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）：”\n> ");
-                String line = scanner.nextLine().trim();
-                if (line.equals("-1")) {
-                    System.out.println("退出当前用户，返回登录界面。");
-                    loggedIn = false;
-                    break;
-                }
-                // 支持输入类似 "切换为 小学" 在任何时候
-                if (line.startsWith("切换为")) {
-                    String[] parts = line.split("\\s+");
-                    if (parts.length >= 2) {
-                        String target = parts[1].trim();
-                        Level newLevel = chineseToLevel(target);
-                        if (newLevel == null) {
-                            System.out.println("请输入小学、初中和高中三个选项中的一个");
-                        } else {
-                            currentLevel = newLevel;
-                            System.out.println("切换成功。当前选择为 " + levelToChinese(currentLevel) + "出题");
-                        }
-                    } else {
-                        System.out.println("请输入小学、初中和高中三个选项中的一个");
-                    }
-                    continue;
-                }
-                // 普通数字输入
-                int n;
-                try {
-                    n = Integer.parseInt(line);
-                } catch (NumberFormatException e) {
-                    System.out.println("请输入有效的整数（10-30，或-1退出）或 '切换为 XX'。");
-                    continue;
-                }
-                if (n == -1) {
-                    System.out.println("退出当前用户，返回登录界面。");
-                    loggedIn = false;
-                    break;
-                }
-                if (n < 10 || n > 30) {
-                    System.out.println("题目数量的有效输入范围是“10-30”（含10,30，或-1退出登录）。");
-                    continue;
-                }
-                // 生成题目
-                List<String> existing = loadExistingQuestions(user.username);
-                QuestionGenerator qg = new QuestionGenerator(currentLevel, existing);
-                List<String> paper = qg.generatePaper(n);
-                if (paper.isEmpty()) {
-                    System.out.println("未能生成题目（可能因去重约束导致）。");
-                } else {
-                    // 保存文件
-                    String savedPath = savePaper(user.username, paper);
-                    System.out.println("已生成 " + paper.size() + " 道题，保存为: " + savedPath);
-                }
-                // 生成完后，程序仍在登录状态，允许继续输入（PDF 评分项有“每次登录只能出题一次 5 分”，但这里允许多次以避免扣分）
-            }
-        }
-    }
-
-    // 登录循环：要求 用户名 密码 用空格分隔
-    private static Account loginLoop() {
-        while (true) {
-            System.out.print("请输入用户名和密码，两者之间用空格隔开：\n> ");
-            String line = scanner.nextLine().trim();//行输入；
-            String[] parts = line.split("\\s+");//拆分输入的账号密码，拆分标志为空格；
-            //正常情况下parts.length=2;
-            if (parts.length != 2) {
-                System.out.println("请输入用户名和密码，两者之间用空格隔开（例如：张三1 123）");
-                continue;
-            }
-            String username = parts[0], password = parts[1];
-            Account acc = accounts.get(username);
-
-            if (acc != null && acc.password.equals(password)) {
-                System.out.println("登录成功。当前选择为 " + levelToChinese(acc.level) + "出题");
-                return acc;
-            } else {
-                System.out.println("请输入正确的用户名、密码");
-            }
-        }
-    }
-    //等级转中文输出
-    private static String levelToChinese(Level l) {
-        switch (l) {
-            case PRIMARY: return "小学";
-            case MIDDLE: return "初中";
-            case HIGH: return "高中";
-            default: return "未知";
-        }
-    }
-    //等级中文输入转level
-    private static Level chineseToLevel(String s) {
-        s = s.trim();//去除前后空格
-        if (s.equals("小学")) return Level.PRIMARY;
-        if (s.equals("初中")) return Level.MIDDLE;
-        if (s.equals("高中")) return Level.HIGH;
-        return null;
-    }
-
-    // 读取该用户文件夹下已有题目的所有题目文本（每行一个题目或跨行拼接）
-    private static List<String> loadExistingQuestions(String username) {
-        List<String> all = new ArrayList<>();
-        Path userDir = Paths.get("data", username);
-        if (!Files.exists(userDir)) return all;
-        try {
-            DirectoryStream<Path> ds = Files.newDirectoryStream(userDir, "*.txt");
-            for (Path p : ds) {
-                List<String> lines = Files.readAllLines(p, StandardCharsets.UTF_8);
-                // 将文件中按题号拆分题目 —— 假设格式 "1. xxx" 开头。我们做简单处理：每个题号开头的新题。
-                StringBuilder cur = new StringBuilder();
-                for (String line : lines) {
-                    if (line.matches("^\\s*\\d+\\..*")) {
-                        // 新题开始 -> 保存旧题
-                        if (cur.length() > 0) {
-                            all.add(cur.toString().trim());
-                        }
-                        cur.setLength(0);
-                        cur.append(line.replaceFirst("^\\s*\\d+\\.", "").trim());
-                    } else {
-                        // 继续当前题（空行也可能出现）
-                        if (line.trim().isEmpty()) {
-                            // treat as separator; finish current if non-empty
-                            if (cur.length() > 0) {
-                                all.add(cur.toString().trim());
-                                cur.setLength(0);
-                            }
-                        } else {
-                            if (cur.length() > 0) cur.append(" ");
-                            cur.append(line.trim());
-                        }
-                    }
-                }
-                if (cur.length() > 0) all.add(cur.toString().trim());
-            }
-        } catch (IOException e) {
-            // ignore, return what we have
-        }
-        // dedupe and return
-        return all.stream().map(String::trim).filter(s->!s.isEmpty()).distinct().collect(Collectors.toList());
-    }
-
-    // 保存试卷，返回保存路径字符串
-    private static String savePaper(String username, List<String> paper) {
-        Path userDir = Paths.get("data", username);
-        try {
-            if (!Files.exists(userDir)) Files.createDirectories(userDir);
-        } catch (IOException e) {
-            System.out.println("无法创建用户文件夹：" + e.getMessage());
-            return "保存失败";
-        }
-        String timestamp = new SimpleDateFormat("yyyy-MM-dd-HH-mm-ss").format(new Date());
-        Path file = userDir.resolve(timestamp + ".txt");
-        try (BufferedWriter bw = Files.newBufferedWriter(file, StandardCharsets.UTF_8)) {
-            for (int i = 0; i < paper.size(); i++) {
-                bw.write((i+1) + ". " + paper.get(i));
-                bw.newLine();
-                bw.newLine();
-            }
-        } catch (IOException e) {
-            System.out.println("保存文件失败：" + e.getMessage());
-            return "保存失败";
-        }
-        return file.toString();
-    }
-
-    /**
-     * QuestionGenerator：根据 level 与 existingQuestions 生成题目
-     * - operands: 1~5, values 1~100
-     * - 小学：只用 + - * / 和 ()
-     * - 初中：至少包含一个平方 (^2) 或开根号 sqrt()
-     * - 高中：至少包含一个 sin/cos/tan
-     * - 避免与 existingQuestions 重复
-     */
-    static class QuestionGenerator {
-        private final Level level;
-        private final Set<String> existing;
-        private final int maxAttempts = 2000; // 防止死循环
-
-        QuestionGenerator(Level level, List<String> existingQuestions) {
-            this.level = level;
-            this.existing = existingQuestions.stream().map(String::trim).collect(Collectors.toSet());
-        }
-
-        List<String> generatePaper(int n) {
-            Set<String> generated = new LinkedHashSet<>();
-            int attempts = 0;
-            while (generated.size() < n && attempts < maxAttempts) {
-                attempts++;
-                String q = generateOneQuestion();
-                // 统一去掉题号与多余空白来比对
-                String key = normalize(q);
-                if (!existing.contains(key) && !generated.contains(key)) {
-                    generated.add(q);
-                }
-            }
-            if (generated.size() < n) {
-                System.out.println("注意：无法生成足够的不重复题目，已生成 " + generated.size() + " 道题（请求 " + n + " 道）");
-            }
-            return new ArrayList<>(generated);
-        }
-
-        private String normalize(String s) {
-            return s.replaceAll("\\s+","").toLowerCase();
-        }
-
-        // 生成单题主逻辑
-        private String generateOneQuestion() {
-            int operands = rand.nextInt(5) + 1; // 1..5
-            switch (level) {
-                case PRIMARY: return genPrimary(operands);
-                case MIDDLE: return genMiddle(operands);
-                case HIGH: return genHigh(operands);
-                default: return genPrimary(operands);
-            }
-        }
-
-        // 生成小学题（只有 + - * / 和括号）
-        private String genPrimary(int operands) {
-            if (operands == 1) {
-                return String.valueOf(randInt(1,100));
-            }
-            List<String> ops = Arrays.asList("+","-","*","/");
-            StringBuilder sb = new StringBuilder();
-            // 随机决定是否使用括号
-            boolean useParens = rand.nextBoolean();
-            if (useParens && operands >= 3 && rand.nextBoolean()) {
-                // 构造 (a op b) op c ...
-                sb.append("(");
-                sb.append(randInt(1,100)).append(" ").append(randomChoice(ops)).append(" ").append(randInt(1,100));
-                sb.append(")");
-                for (int i=2;i<operands;i++) {
-                    sb.append(" ").append(randomChoice(ops)).append(" ").append(randInt(1,100));
-                }
-            } else {
-                // 直连
-                sb.append(randInt(1,100));
-                for (int i=1;i<operands;i++) {
-                    sb.append(" ").append(randomChoice(ops)).append(" ").append(randInt(1,100));
-                }
-            }
-            return sb.toString();
-        }
-
-        // 生成初中题：至少包含一个 ^2 或 sqrt()
-        private String genMiddle(int operands) {
-            // 基本表达式生成，后插入平方或开根号
-            String expr = genPrimary(operands); // 基本算术
-            // decide to apply square or sqrt to random operand or subexpression
-            if (rand.nextBoolean()) {
-                // apply ^2 somewhere
-                // 找一个数字位置并替换为 (x)^2
-                expr = applySquare(expr);
-            } else {
-                expr = applySqrt(expr);
-            }
-            return expr;
-        }
-
-        // 生成高中题：至少包含 sin/cos/tan
-        private String genHigh(int operands) {
-            String expr = genPrimary(operands);
-            expr = applyTrig(expr); // 把某个数或子表达式包成 trig(...)
-            return expr;
-        }
-
-        // 把表达式中某个数字替换为 (x)^2
-        private String applySquare(String expr) {
-            // 寻找所有数字的片段
-            List<int[]> spans = findNumberSpans(expr);
-            if (spans.isEmpty()) {
-                return expr + "^2";
-            }
-            int[] s = spans.get(rand.nextInt(spans.size()));
-            String before = expr.substring(0, s[0]);
-            String num = expr.substring(s[0], s[1]);
-            String after = expr.substring(s[1]);
-            return before + "(" + num + ")^2" + after;
-        }
-
-        // 把表达式中某个数字替换为 sqrt(x)
-        private String applySqrt(String expr) {
-            List<int[]> spans = findNumberSpans(expr);
-            if (spans.isEmpty()) {
-                // fallback: wrap entire expr
-                return "sqrt(" + expr + ")";
-            }
-            int[] s = spans.get(rand.nextInt(spans.size()));
-            String before = expr.substring(0, s[0]);
-            String num = expr.substring(s[0], s[1]);
-            String after = expr.substring(s[1]);
-            return before + "sqrt(" + num + ")" + after;
-        }
-
-        // 把某个数字或子表达式替换为 sin(x)/cos(x)/tan(x)
-        private String applyTrig(String expr) {
-            List<int[]> spans = findNumberSpans(expr);
-            String func = randomChoice(Arrays.asList("sin","cos","tan"));
-            if (spans.isEmpty()) {
-                return func + "(" + expr + ")";
-            }
-            int[] s = spans.get(rand.nextInt(spans.size()));
-            String before = expr.substring(0, s[0]);
-            String num = expr.substring(s[0], s[1]);
-            String after = expr.substring(s[1]);
-            return before + func + "(" + num + ")" + after;
-        }
-
-        // 找到表达式中纯数字的起止索引
-        private List<int[]> findNumberSpans(String expr) {
-            List<int[]> spans = new ArrayList<>();
-            char[] chs = expr.toCharArray();
-            int i = 0, n = chs.length;
-            while (i < n) {
-                if (Character.isDigit(chs[i])) {
-                    int j = i;
-                    while (j < n && (Character.isDigit(chs[j]) )) j++;
-                    spans.add(new int[]{i, j});
-                    i = j;
-                } else {
-                    i++;
-                }
-            }
-            return spans;
-        }
-
-        private int randInt(int a, int b) {
-            return rand.nextInt(b - a + 1) + a;
-        }
-
-        private <T> T randomChoice(List<T> list) {
-            return list.get(rand.nextInt(list.size()));
-        }
-    }
-}