diff --git a/src/SUMMARY.md b/src/SUMMARY.md
index a332c63f9..f196bf079 100644
--- a/src/SUMMARY.md
+++ b/src/SUMMARY.md
@@ -406,5 +406,6 @@
     - [机器人活动区域 - DFS](od/2024e200/moving-area-of-robot/index.md)
     - [简易压缩算法/一种字符串压缩表示的解压 - 字符串](od/2024e200/compress-string/index.md)
     - [智能驾驶 - 二分查找](od/2024e200/intelligent-driving/index.md)
+    - [字符串拼接 - 字符串](od/2024e200/merge-string/index.md)
 
 [参考资料](refs.md)
diff --git a/src/od/2024e100/height-of-ternary-tree/src/main.rs b/src/od/2024e100/height-of-ternary-tree/src/main.rs
index 990447dfb..4c6c1aadd 100644
--- a/src/od/2024e100/height-of-ternary-tree/src/main.rs
+++ b/src/od/2024e100/height-of-ternary-tree/src/main.rs
@@ -91,7 +91,7 @@ fn main() {
     let ret = stdin().lock().read_line(&mut line);
     assert!(ret.is_ok());
     let num_nodes: usize = line.trim().parse().unwrap();
-    assert!(1 <= num_nodes && num_nodes <= 10000);
+    assert!((1..=10000).contains(&num_nodes));
 
     // 读取所有节点的值, 存放到数组
     line.clear();
diff --git a/src/od/2024e100/vlan/src/main.rs b/src/od/2024e100/vlan/src/main.rs
index 3602b8f49..ff05d9875 100644
--- a/src/od/2024e100/vlan/src/main.rs
+++ b/src/od/2024e100/vlan/src/main.rs
@@ -21,12 +21,12 @@ fn solution() {
             let end_id: u32 = range_part.next().unwrap().parse().unwrap();
             assert!(range_part.next().is_none());
             for vlan_id in start_id..=end_id {
-                assert!(1 <= vlan_id && vlan_id <= 4094);
+                assert!((1..=4094).contains(&vlan_id));
                 id_set.insert(vlan_id);
             }
         } else {
             let vlan_id: u32 = part.parse().unwrap();
-            assert!(1 <= vlan_id && vlan_id <= 4094);
+            assert!((1..=4094).contains(&vlan_id));
             id_set.insert(vlan_id);
         }
     }
diff --git a/src/od/2024e200/filesystem/src/main.rs b/src/od/2024e200/filesystem/src/main.rs
index c8566b3cf..811b40c40 100644
--- a/src/od/2024e200/filesystem/src/main.rs
+++ b/src/od/2024e200/filesystem/src/main.rs
@@ -62,7 +62,7 @@ impl FolderEntry {
             return None;
         }
         if self.children.contains(folder_name) {
-            let path = Self::to_path(&self.path, &folder_name);
+            let path = Self::to_path(&self.path, folder_name);
             Some(path)
         } else {
             None
@@ -92,7 +92,7 @@ fn solution() {
             Some("cd") => {
                 // 切换工作目录
                 if let Some(folder_name) = parts.next() {
-                    if !parts.next().is_none() {
+                    if parts.next().is_some() {
                         continue;
                     }
                     if let Some(cwd_entry) = map.get_mut(&cwd) {
@@ -105,7 +105,7 @@ fn solution() {
             Some("mkdir") => {
                 // 创建子目录
                 if let Some(folder_name) = parts.next() {
-                    if !parts.next().is_none() {
+                    if parts.next().is_some() {
                         continue;
                     }
                     if let Some(cwd_entry) = map.get_mut(&cwd) {
diff --git a/src/od/2024e200/index.md b/src/od/2024e200/index.md
index 613e4c6ac..8dd4422ed 100644
--- a/src/od/2024e200/index.md
+++ b/src/od/2024e200/index.md
@@ -22,3 +22,4 @@
 20. [机器人活动区域 - DFS](moving-area-of-robot/index.md)
 21. [简易压缩算法/一种字符串压缩表示的解压 - 字符串](compress-string/index.md)
 22. [智能驾驶 - 二分查找](intelligent-driving/index.md)
+23. [字符串拼接 - 字符串](merge-string/index.md)
diff --git a/src/od/2024e200/merge-string/Cargo.toml b/src/od/2024e200/merge-string/Cargo.toml
new file mode 100644
index 000000000..aebc92686
--- /dev/null
+++ b/src/od/2024e200/merge-string/Cargo.toml
@@ -0,0 +1,7 @@
+[package]
+name = "e200-merge-string"
+version = "0.1.0"
+edition = "2021"
+publish = false
+
+[dependencies]
diff --git a/src/od/2024e200/merge-string/assets/input1.txt b/src/od/2024e200/merge-string/assets/input1.txt
new file mode 100644
index 000000000..603ef6237
--- /dev/null
+++ b/src/od/2024e200/merge-string/assets/input1.txt
@@ -0,0 +1 @@
+aab 2
\ No newline at end of file
diff --git a/src/od/2024e200/merge-string/assets/input2.txt b/src/od/2024e200/merge-string/assets/input2.txt
new file mode 100644
index 000000000..6275e17fd
--- /dev/null
+++ b/src/od/2024e200/merge-string/assets/input2.txt
@@ -0,0 +1 @@
+abc 2
\ No newline at end of file
diff --git a/src/od/2024e200/merge-string/assets/output1.txt b/src/od/2024e200/merge-string/assets/output1.txt
new file mode 100644
index 000000000..d8263ee98
--- /dev/null
+++ b/src/od/2024e200/merge-string/assets/output1.txt
@@ -0,0 +1 @@
+2
\ No newline at end of file
diff --git a/src/od/2024e200/merge-string/assets/output2.txt b/src/od/2024e200/merge-string/assets/output2.txt
new file mode 100644
index 000000000..62f945751
--- /dev/null
+++ b/src/od/2024e200/merge-string/assets/output2.txt
@@ -0,0 +1 @@
+6
\ No newline at end of file
diff --git a/src/od/2024e200/merge-string/index.md b/src/od/2024e200/merge-string/index.md
new file mode 100644
index 000000000..6e8e18b09
--- /dev/null
+++ b/src/od/2024e200/merge-string/index.md
@@ -0,0 +1,52 @@
+# 字符串拼接
+
+## 题目描述
+
+构成指定长度字符串的个数.
+
+给定 M (0 < M ≤ 30) 个字符 (a-z) , 从中取出任意字符 (每个字符只能用一次) 拼接成长度为 N (0 < N ≤ 5) 的字符串,
+要求相同的字符不能相邻, 计算出给定的字符列表能拼接出多少种满足条件的字符串.
+
+输入非法或者无法拼接出满足条件的字符串则返回0.
+
+### 输入描述
+
+给定的字符列表和结果字符串长度, 中间使用空格 ` ` 拼接
+
+### 输出描述
+
+满足条件的字符串个数.
+
+### 示例1
+
+输入:
+
+```text
+{{#include assets/input1.txt}}
+```
+
+输出:
+
+```text
+{{#include assets/output1.txt}}
+```
+
+说明: 只能构成ab, ba.
+
+### 示例2
+
+输入:
+
+```text
+{{#include assets/input2.txt}}
+```
+
+输出:
+
+```text
+{{#include assets/output2.txt}}
+```
+
+说明: 可以构成 ab ac ba bc ca cb.
+
+## 题解
diff --git a/src/od/2024e200/merge-string/src/main.rs b/src/od/2024e200/merge-string/src/main.rs
new file mode 100644
index 000000000..e7a11a969
--- /dev/null
+++ b/src/od/2024e200/merge-string/src/main.rs
@@ -0,0 +1,3 @@
+fn main() {
+    println!("Hello, world!");
+}