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PegasusWang · PegasusWang · commit fd4035a35061 · 2018-12-19T08:37:09.000+08:00
diff --git a/docs/14_树与二叉树/tree.md b/docs/14_树与二叉树/tree.md
@@ -202,7 +202,7 @@ btree.preorder_trav(btree.root)    # 输出 A, B, D, E, H, C, F, G, I, J
 
 ```py
     def layer_trav(self, subtree):
-        cur_nodes = [subtree]
+        cur_nodes = [subtree]  # current layer nodes
         next_nodes = []
         while cur_nodes or next_nodes:
             for node in cur_nodes:
