fix(tree-diameter.md): 修改了例题的格式

diff --git a/docs/graph/tree-diameter.md b/docs/graph/tree-diameter.md
index 7fd0ca4..12edd1a 100644 (file)
--- a/docs/graph/tree-diameter.md
+++ b/docs/graph/tree-diameter.md
@@ -4,7 +4,8 @@
 
 ## 例题
 
-例题 [SPOJ PT07Z, Longest path in a tree](https://www.spoj.com/problems/PT07Z/) 。
+???+note "[SPOJ PT07Z, Longest path in a tree](https://www.spoj.com/problems/PT07Z/)"
+    给定一棵 $n$ 个节点的树，求其直径的长度。$1\leq n\leq 10^4$。
 
 ## 做法 1. 两次 DFS