diff --git a/.gitignore b/.gitignore
index 9dceef81..c81a4e17 100644
--- a/.gitignore
+++ b/.gitignore
@@ -10,3 +10,5 @@ tests/data/
 tests/my_*.py
 docs/build/
 .pdm-python
+*.egg-info
+*.ipynb
\ No newline at end of file
diff --git a/aiopenapi3/openapi.py b/aiopenapi3/openapi.py
index 9c2689d2..7038897f 100644
--- a/aiopenapi3/openapi.py
+++ b/aiopenapi3/openapi.py
@@ -397,66 +397,43 @@ def _init_operationindex(self, use_operation_tags: bool):
         self._operationindex = OperationIndex(self, use_operation_tags)
 
     @staticmethod
-    def _iterate_schemas(schemas: Dict[int, "SchemaType"], next: Set[int], processed: Set[int]):
-        """
-        recursively collect all schemas related to the starting set
-        """
-        if not next:
-            return processed
-
-        processed.update(next)
-
-        def not_in_processed(z: Tuple[int, SchemaBase]) -> TypeGuard[Tuple[int, "SchemaType"]]:
-            return z[0] not in processed
-
-        def is_instance_schema_ref(
-            x: Union["SchemaType", "ReferenceType"]
-        ) -> TypeGuard[Union["SchemaType", "ReferenceType"]]:
-            return isinstance(x, (ReferenceBase, SchemaBase))
-
-        new: Dict[int, "SchemaType"] = cast(
-            Dict[int, "SchemaType"],
-            collections.ChainMap(
-                *[
-                    dict(
-                        filter(
-                            not_in_processed,
-                            map(
-                                lambda y: (id(y._target), y._target) if isinstance(y, ReferenceBase) else (id(y), y),
-                                filter(
-                                    is_instance_schema_ref,
-                                    getattr(schemas[i], "oneOf", [])  # Swagger compat
-                                    + getattr(schemas[i], "anyOf", [])  # Swagger compat
-                                    + schemas[i].allOf
-                                    + list(schemas[i].properties.values())
-                                    + (
-                                        [schemas[i].items]
-                                        if schemas[i].type == "array"
-                                        and schemas[i].items
-                                        and not isinstance(schemas[i].items, list)
-                                        else []
-                                    )
-                                    + (
-                                        schemas[i].items
-                                        if schemas[i].type == "array"
-                                        and schemas[i].items
-                                        and isinstance(schemas[i].items, list)
-                                        else []
-                                    ),
-                                ),  # type: ignore[operator]
-                            ),
-                        )
-                    )  # type: ignore[arg-type]
-                    for i in next
-                ]
-            ),
+    def _get_combined_attributes(schema):
+        """Combine attributes from the schema."""
+        return (
+            getattr(schema, "oneOf", [])  # Swagger compat
+            + getattr(schema, "anyOf", [])  # Swagger compat
+            + schema.allOf
+            + list(schema.properties.values())
+            + ([schema.items] if schema.type == "array" and schema.items and not isinstance(schema, list) else [])
+            + (schema.items if schema.type == "array" and schema.items and isinstance(schema, list) else [])
         )
 
-        sets = set(new.keys())
-        schemas.update(new)
-        processed.update(sets)
+    @classmethod
+    def _process_schema_attributes(cls, schema, processed):
+        """Process attributes of a schema and filter out the processed ones."""
+        combined_attributes = cls._get_combined_attributes(schema)
+        return {
+            id(item._target)
+            if isinstance(item, ReferenceBase)
+            else id(item): item._target
+            if isinstance(item, ReferenceBase)
+            else item
+            for item in combined_attributes
+            if isinstance(item, (ReferenceBase, SchemaBase)) and id(item) not in processed
+        }
 
-        return OpenAPI._iterate_schemas(schemas, sets, processed)
+    @classmethod
+    def _iterate_schemas(cls, schemas: dict, next_set: set, processed: set):
+        """Iteratively collect all schemas related to the starting set."""
+        while next_set:
+            processed.update(next_set)
+            # Using dictionary comprehension to combine the results,
+            # which seems more efficient than ChainMap
+            new = {k: v for i in next_set for k, v in cls._process_schema_attributes(schemas[i], processed).items()}
+            next_set = set(new.keys()) - processed
+            schemas.update(new)
+            processed.update(next_set)
+        return processed
 
     def _init_schema_types_collect(self) -> Dict[str, "SchemaType"]:
         byname: Dict[str, "SchemaType"] = dict()