[fix #484] resolve basic_arithmetic fails when size is large (#485)

* [fix] resolve basic_arithmetic fails when size is large by replacing zero divisor with 1

reasoning_gym/arithmetic/basic_arithmetic.py

@@ -191,6 +191,9 @@ class BasicArithmeticDataset(ProceduralDataset):
                     space_parts.append(" ")
                 space_parts.append(p)
             expression = "".join(space_parts).strip()
+        # Avoid division-by-zero in final evaluation by converting '/0' patterns to '/1'
+        if "/ 0" in expression:
+            expression = expression.replace("/ 0", "/ 1")
         result = eval_floordiv(expression)  # Note: eval is safe here as we control the input
 
         return expression, result

tests/test_basic_arithmetic.py

@@ -168,3 +168,19 @@ def test_basic_arithmetic_curriculum_upper_bound():
     increased_cfg = curriculum.generate_configuration(base_value)
     assert increased_cfg.min_terms == 2 and increased_cfg.max_terms == 3
     assert increased_cfg.min_digits == 1 and increased_cfg.max_digits == 2
+
+
+def test_arithmetic_dataset_large_random_generation():
+    """Stress-test generation of many arithmetic questions to catch random errors"""
+    config = BasicArithmeticDatasetConfig(
+        size=100000,
+        seed=123,
+        min_terms=2,
+        max_terms=6,
+        min_digits=1,
+        max_digits=3,
+    )
+    dataset = BasicArithmeticDataset(config)
+    for item in dataset:
+        assert isinstance(item, dict)
+        assert "question" in item and "answer" in item and "metadata" in item