From c66a7ee3327dc2cb64ce7bf2a89909109f2151af Mon Sep 17 00:00:00 2001
From: small_bear <2421342308@qq.com>
Date: Wed, 27 Nov 2024 00:14:21 +0800
Subject: [PATCH] Update index.md
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit

segment tree2 ’modify‘ bugfix
---
 moonbit-docs/docs/examples/segment-tree2/index.md | 10 +++++++---
 1 file changed, 7 insertions(+), 3 deletions(-)

diff --git a/moonbit-docs/docs/examples/segment-tree2/index.md b/moonbit-docs/docs/examples/segment-tree2/index.md
index 5ea9fa6c..253a9dc4 100644
--- a/moonbit-docs/docs/examples/segment-tree2/index.md
+++ b/moonbit-docs/docs/examples/segment-tree2/index.md
@@ -150,13 +150,17 @@ fn modify(
   modify_r: Int,
   tag: LazyTag
 ) -> Node {
-  if modify_l > r || l > modify_r {
+  if l > r {
+    empty_node
+  } else if modify_l > r || l > modify_r {
     self
   } else if modify_l <= l && modify_r >= r {
     self.apply(tag)
   } else {
-    guard let Node(~left, ~right, ..) = self
-    left.apply(tag) + right.apply(tag)
+    guard let Node(left~, right~, ..) = self
+    let mid = (l + r) >> 1
+    left.modify(l, mid, modify_l, modify_r, tag) + 
+    right.modify(mid+1, r, modify_l, modify_r, tag)
   }
 }
 ```