Move us to HashSet to avoid the overhead of tracking the order
diff --git a/examples/stocks/lib/main.dart b/examples/stocks/lib/main.dart
index 4b235cd..cfc1b4a 100644
--- a/examples/stocks/lib/main.dart
+++ b/examples/stocks/lib/main.dart
@@ -5,6 +5,7 @@
 library stocks;
 
 import 'dart:async';
+import 'dart:collection';
 import 'dart:math' as math;
 import 'dart:ui' as ui;