diff --git a/src/Middleproblem.java b/src/Middleproblem.java
new file mode 100644
index 0000000..f79303e
--- /dev/null
+++ b/src/Middleproblem.java
@@ -0,0 +1,119 @@
+import java.util.Random;
+import java.util.Scanner;
+
+public class Middleproblem implements Makeproblem {
+  private Random random = new Random();
+  static int basic = 1;
+  String name = "1";
+  String time = "1";
+  int num = 1;
+
+  public static void main(String[] args) {
+    for (int i = 0; i < 15; i++) {
+      basic = 1;
+      Middleproblem m1 = new Middleproblem();
+      System.out.println((i + 1) + ". " + m1.generateSmartExpression());
+    }
+  }
+
+  void start(int num, String username) {
+    name = username;
+    Timemanage t1 = new Timemanage();
+    time = t1.timeget();
+    for (int i = 0; i < num; i++) {
+      basic = 1;
+      System.out.println((i + 1) + ". " + generateSmartExpression());
+      System.out.println("");
+    }
+  }
+
+  @Override
+  public String generateSmartExpression() {
+    int operatorCount = random.nextInt(3) + 1;
+    int b2 = random.nextInt(operatorCount) + 1;
+    String file = time;
+    String result;
+    while (true) {
+      int flag = 0;
+      result = buildExpression(operatorCount, b2);
+      filemanage f1 = new filemanage();
+      f1.fileread(name);
+      f1.fileread(name);
+      for (String i : f1.array) {
+        String[] parts = i.split("\\.", 2);
+        String j = parts.length > 1 ? parts[1] : i;
+        if (result.equals(j)) {
+          flag = 1;
+        }
+      }
+      if (flag == 1) {
+        continue;
+      }
+      f1.filecreate(name, file);
+      f1.filewrite(name, file, num + "." + result);
+      f1.filewrite(name, file, " ");
+      num++;
+      break;
+    }
+    return result;
+  }
+
+  @Override
+  public String buildExpression(int operatorCount, int b2) {
+    if (operatorCount == 1) {
+      return generateSimpleExpression(b2);
+    }
+
+    // 随机决定分割点来添加括号
+    int splitPoint = random.nextInt(operatorCount - 1) + 1;
+
+    String leftPart = (splitPoint > 1 && random.nextBoolean()) ?
+            "(" + buildExpression(splitPoint, b2) + ")" :
+            buildExpression(splitPoint, b2);
+
+    String rightPart = (operatorCount - splitPoint > 1 && random.nextBoolean()) ?
+            "(" + buildExpression(operatorCount - splitPoint, b2) + ")" :
+            buildExpression(operatorCount - splitPoint, b2);
+
+    char operator = getRandomOperator("+-*/");
+    return leftPart + " " + operator + " " + rightPart;
+  }
+
+  @Override
+  public String generateSimpleExpression(int b2) {
+    int a = random.nextInt(100) + 1;
+    int b = random.nextInt(100) + 1;
+    char op = getRandomOperator("+-*/√²");
+    if (basic == b2) {
+      op = getRandomOperator("√²");
+      if (op == '√') {
+        basic = 0;
+        return op + "" + b;
+      } else if (op == '²') {
+        basic = 0;
+        return a + "" + op;
+      }
+    } else {
+      basic++;
+    }
+    if (random.nextInt(2) == 0) {
+      return a + "";
+    }
+    if (op == '√') {
+      return op + "" + b;
+    } else if (op == '²') {
+      return a + "" + op;
+    } else {
+      if (random.nextBoolean()) {
+        return a + " " + op + " " + b;
+      } else {
+        return "(" + a + " " + op + " " + b + ")";
+      }
+    }
+  }
+
+  @Override
+  public char getRandomOperator(String operators) {
+    return operators.charAt(random.nextInt(operators.length()));
+  }
+}