diff --git a/sik9252/AddBinary.js b/sik9252/AddBinary.js
new file mode 100644
index 0000000..a2845e1
--- /dev/null
+++ b/sik9252/AddBinary.js
@@ -0,0 +1,8 @@
+/**
+ * @param {string} a
+ * @param {string} b
+ * @return {string}
+ */
+var addBinary = function (a, b) {
+  return (BigInt("0b" + a) + BigInt("0b" + b)).toString(2);
+};
diff --git a/sik9252/DiameterOfBinaryTree.js b/sik9252/DiameterOfBinaryTree.js
new file mode 100644
index 0000000..dc9f6ec
--- /dev/null
+++ b/sik9252/DiameterOfBinaryTree.js
@@ -0,0 +1,21 @@
+/**
+ * @param {TreeNode} root
+ * @return {number}
+ */
+var diameterOfBinaryTree = function (root) {
+  let diameter = 0;
+
+  function dfs(node) {
+    if (!node) return 0;
+
+    const left = dfs(node.left);
+    const right = dfs(node.right);
+
+    diameter = Math.max(diameter, left + right);
+
+    return Math.max(left, right) + 1;
+  }
+
+  dfs(root);
+  return diameter;
+};