diff --git a/TangDou/Topic/【换根DP】专题.md b/TangDou/Topic/【换根DP】专题.md
index 1fc37d6..828e39e 100644
--- a/TangDou/Topic/【换根DP】专题.md
+++ b/TangDou/Topic/【换根DP】专题.md
@@ -1269,6 +1269,8 @@ signed main() {
 }
 ```
 #### [$V-Subtree$](https://www.luogu.com.cn/problem/AT_dp_v)
+https://blog.csdn.net/Emm_Titan/article/details/123875298
+
 **题意**
 给定一棵 $N$ 个节点的树，现在需要将每一个节点染成黑色或白色。