Update solver_factorial.py

solver_factorial.py

@@ -9,15 +9,26 @@ from models import SolverResult
 
 def solve_factorial(text: str) -> Optional[SolverResult]:
     raw = text or ""
-    lower = raw.lower()
+    lower = raw.lower().strip()
 
-    if "!" not in raw and "factorial" not in lower and "trailing zero" not in lower:
+    if not raw:
+        return None
+
+    has_factorial_notation = re.search(r"(\d+)\s*!", raw) is not None
+    has_factorial_word = "factorial" in lower
+    has_trailing_zero_phrase = "trailing zero" in lower or "trailing zeros" in lower
+
+    if not (has_factorial_notation or has_factorial_word or has_trailing_zero_phrase):
         return None
 
     # trailing zeros in n!
-    m = re.search(r"trailing zeros?.*?(\d+)\s*!", lower)
-    if m:
-        n = int(m.group(1))
+    trailing_match = re.search(
+        r"trailing zeros?.*?(?:in|of)?\s*(\d+)\s*!",
+        lower
+    )
+    if trailing_match:
+        n = int(trailing_match.group(1))
+
         count = 0
         power = 5
         while power <= n:
@@ -28,28 +39,32 @@ def solve_factorial(text: str) -> Optional[SolverResult]:
             domain="quant",
             solved=True,
             topic="factorial_trailing_zeros",
-            answer_value=str(count),
+            answer_value=None,
             internal_answer=str(count),
             steps=[
                 "Trailing zeros come from factors of 10.",
-                "Each 10 contributes one 2 and one 5.",
-                "In factorials, 5s are the limiting factor, so count factors of 5.",
+                "Each factor of 10 is made from one 2 and one 5.",
+                "In a factorial, there are usually more 2s than 5s, so count the number of factors of 5.",
+                "Count multiples of 5, then add extra 5s from numbers like 25, 125, and so on.",
             ],
         )
 
     # direct factorial value
-    m = re.search(r"(\d+)\s*!", raw)
-    if m:
-        n = int(m.group(1))
+    factorial_match = re.search(r"(\d+)\s*!", raw)
+    if factorial_match:
+        n = int(factorial_match.group(1))
         result = math.factorial(n)
+
         return SolverResult(
             domain="quant",
             solved=True,
             topic="factorial",
-            answer_value=str(result),
+            answer_value=None,
             internal_answer=str(result),
             steps=[
-                "Expand the factorial as descending multiplication.",
+                "A factorial means multiply descending whole numbers from that number down to 1.",
+                "Write the expression as repeated multiplication.",
+                "Then simplify carefully step by step.",
             ],
         )