修改小学题目出题逻辑,保证至少两个操作数

src/com/personalproject/generator/PrimaryQuestionGenerator.java

@@ -10,7 +10,8 @@ public final class PrimaryQuestionGenerator implements QuestionGenerator {
 
   @Override
   public String generateQuestion(Random random) {
-    int operandCount = random.nextInt(5) + 1;
+    // 至少生成两个操作数，避免题目退化成单个数字
+    int operandCount = random.nextInt(4) + 2;
     StringBuilder builder = new StringBuilder();
     for (int index = 0; index < operandCount; index++) {
       if (index > 0) {