diff --git a/climbing-stairs-70/src/main.rs b/climbing-stairs-70/src/main.rs
index 51757c0..589637a 100644
--- a/climbing-stairs-70/src/main.rs
+++ b/climbing-stairs-70/src/main.rs
@@ -1,3 +1,4 @@
+#[allow(dead_code)]
 fn climb_stairs_on2(n: i32) -> i32 {
     if n == 1 {
         return 1;
diff --git a/maximum-depth-of-binary-tree-104/src/main.rs b/maximum-depth-of-binary-tree-104/src/main.rs
index a6d5854..7793427 100644
--- a/maximum-depth-of-binary-tree-104/src/main.rs
+++ b/maximum-depth-of-binary-tree-104/src/main.rs
@@ -35,6 +35,34 @@ impl Solution {
     }
 }
 
-fn main() {
-    println!("Hello, world!");
+fn test_max_depth() {
+    use std::cell::RefCell;
+    use std::rc::Rc;
+
+    // Helper function to create a TreeNode
+    fn new_node(
+        val: i32,
+        left: Option<Rc<RefCell<TreeNode>>>,
+        right: Option<Rc<RefCell<TreeNode>>>,
+    ) -> Option<Rc<RefCell<TreeNode>>> {
+        Some(Rc::new(RefCell::new(TreeNode { val, left, right })))
+    }
+
+    // Constructing a simple tree:
+    //       1
+    //      / \
+    //     2   3
+    //    /
+    //   4
+    let tree = new_node(
+        1,
+        new_node(2, new_node(4, None, None), None),
+        new_node(3, None, None),
+    );
+
+    assert_eq!(Solution::max_depth(tree), 3);
+}
+
+fn main() {
+    println!("{:?}", test_max_depth());
 }
diff --git a/merge-two-sorted-lists-21/src/main.rs b/merge-two-sorted-lists-21/src/main.rs
index 0f306ca..636cfa8 100644
--- a/merge-two-sorted-lists-21/src/main.rs
+++ b/merge-two-sorted-lists-21/src/main.rs
@@ -11,6 +11,7 @@ pub struct ListNode {
 
 impl ListNode {
     #[inline]
+    #[allow(dead_code)]
     fn new(val: i32) -> Self {
         ListNode { next: None, val }
     }