完成ACM ContestProblem相关判题逻辑

contest,submission等表默认-create_time排序

utils/api/api.py

@@ -130,7 +130,7 @@ class APIView(View):
             count = query_set.count()
             results = object_serializer(results, many=True).data
         else:
-            count = len(query_set)
+            count = query_set.count()
         data = {"results": results,
                 "total": count}
         return data