ADD file via upload

src/PrimaryQuestionGenerator.java

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+public class PrimaryQuestionGenerator extends AbstractQuestionGenerator {
+    private static final String[] OPERATORS = {"+", "-", "×", "÷"};
+    
+    @Override
+    public String generateQuestion() {
+        int attempts = 0;
+        while (attempts < 100) {
+            attempts++; 
+            int operandCount = random.nextInt(4) + 2; // 2~5个操作数
+            StringBuilder question = new StringBuilder();
+            
+            // 生成操作数和运算符
+            for (int i = 0; i < operandCount; i++) {
+                question.append(generateNumber());
+                if (i < operandCount - 1) {
+                    question.append(" ").append(generateOperator(OPERATORS)).append(" ");
+                }
+            }
+            // 随机添加括号
+            String result = addReasonableParentheses(question.toString(), operandCount);
+            result = ensureBalancedParentheses(result); // 确保括号平衡
+            
+            if (isQuestionUnique(result) && isValidParentheses(result) && hasOperator(result)) {
+                addToGeneratedQuestions(result);
+                String regex = "(?<!\\s)\\)(?=[^)]*$)";
+                result = result.replaceAll(regex, " )");
+                return result;
+            }
+        }
+        return "3 + 5"; // 备用题目
+    }
+    
+    private String addReasonableParentheses(String expression, int operandCount) {
+    	if (operandCount <= 2 || random.nextDouble() < 0.3) {
+            return expression;
+        }
+        
+        String[] parts = expression.split(" ");
+        if (parts.length < 5) return expression;
+        
+        StringBuilder newExpr = new StringBuilder();
+        
+        int start = random.nextInt(parts.length / 2);
+        int end = start + random.nextInt(parts.length / 2 - start + 1) + 1;
+        end = Math.min(end, parts.length / 2 - 1);
+        
+        for (int i = 0; i < parts.length; i++) {
+            if (i == start * 2) {
+                newExpr.append("( ");
+            }
+            newExpr.append(parts[i]);
+            
+            if (i == end * 2 && i >= start * 2 + 2) {
+                newExpr.append(" )");
+            }
+            if (i < parts.length - 1) {
+                newExpr.append(" ");
+            }
+        }
+        
+        return newExpr.toString().trim();
+    }
+    
+}