diff --git a/graphs_trees/graph_bfs/bfs_solution.ipynb b/graphs_trees/graph_bfs/bfs_solution.ipynb
index 1825f0b..4f1090f 100644
--- a/graphs_trees/graph_bfs/bfs_solution.ipynb
+++ b/graphs_trees/graph_bfs/bfs_solution.ipynb
@@ -116,14 +116,14 @@
     "        return\n",
     "    queue = deque()\n",
     "    queue.append(root)\n",
-    "    root.visited = True\n",
+    "    root.visit_state = State.visited\n",
     "    while queue:\n",
     "        node = queue.popleft()\n",
     "        visit_func(node)\n",
     "        for adjacent_node in node.adjacent:\n",
-    "            if not adjacent_node.visited:\n",
+    "            if adjacent_node.visit_state == State.unvisited:\n",
     "                queue.append(adjacent_node)\n",
-    "                adjacent_node.visited = True"
+    "                adjacent_node.visit_state = State.visited"
    ]
   },
   {
diff --git a/graphs_trees/graph_dfs/dfs_solution.ipynb b/graphs_trees/graph_dfs/dfs_solution.ipynb
index 3f7f59b..3f50459 100644
--- a/graphs_trees/graph_dfs/dfs_solution.ipynb
+++ b/graphs_trees/graph_dfs/dfs_solution.ipynb
@@ -110,9 +110,9 @@
     "    if root is None:\n",
     "        return\n",
     "    visit_func(root)\n",
-    "    root.visited = True\n",
+    "    root.visit_state = State.visited\n",
     "    for node in root.adjacent:\n",
-    "        if not node.visited:\n",
+    "        if node.visit_state == State.unvisited:\n",
     "            dfs(node, visit_func)"
    ]
   },
diff --git a/graphs_trees/graph_path_exists/path_exists_solution.ipynb b/graphs_trees/graph_path_exists/path_exists_solution.ipynb
index 2610c72..378d046 100644
--- a/graphs_trees/graph_path_exists/path_exists_solution.ipynb
+++ b/graphs_trees/graph_path_exists/path_exists_solution.ipynb
@@ -127,7 +127,7 @@
     "        return True\n",
     "    queue = deque()\n",
     "    queue.append(start)\n",
-    "    start.visited = True\n",
+    "    start.visit_state = State.visited\n",
     "    while queue:\n",
     "        node = queue.popleft()\n",
     "        if node is None:\n",
@@ -135,9 +135,9 @@
     "        if node is end:\n",
     "            return True\n",
     "        for adj_node in node.adjacent:\n",
-    "            if not adj_node.visited:\n",
+    "            if adj_node.visit_state == State.unvisited:\n",
     "                queue.append(adj_node)\n",
-    "                adj_node.visited = True\n",
+    "                adj_node.visit_state = State.visited\n",
     "    return False"
    ]
   },