diff --git a/solutions/system_design/social_graph/social_graph_snippets.py b/solutions/system_design/social_graph/social_graph_snippets.py
index 8a83f74..f0ea4c4 100644
--- a/solutions/system_design/social_graph/social_graph_snippets.py
+++ b/solutions/system_design/social_graph/social_graph_snippets.py
@@ -1,5 +1,11 @@
 # -*- coding: utf-8 -*-
 from collections import deque
+from enum import Enum
+
+
+class State(Enum):
+    unvisited = 0
+    visited = 1
 
 
 class Graph(object):