diff --git a/sik9252/BalancedBinaryTree.js b/sik9252/BalancedBinaryTree.js
new file mode 100644
index 0000000..f5c48c6
--- /dev/null
+++ b/sik9252/BalancedBinaryTree.js
@@ -0,0 +1,19 @@
+var isBalanced = function (root) {
+  function getHeight(node) {
+    if (node === null) return 0;
+    return Math.max(getHeight(node.left), getHeight(node.right)) + 1;
+  }
+
+  function check(node) {
+    if (node === null) return true;
+
+    const leftH = getHeight(node.left);
+    const rightH = getHeight(node.right);
+
+    if (Math.abs(leftH - rightH) > 1) return false;
+
+    return check(node.left) && check(node.right);
+  }
+
+  return check(root);
+};
diff --git a/sik9252/ImplementQueueUsingStacks.js b/sik9252/ImplementQueueUsingStacks.js
new file mode 100644
index 0000000..9e40280
--- /dev/null
+++ b/sik9252/ImplementQueueUsingStacks.js
@@ -0,0 +1,57 @@
+var MyQueue = function () {
+  this.stack = [];
+};
+
+/**
+ * @param {number} x
+ * @return {void}
+ */
+MyQueue.prototype.push = function (x) {
+  this.stack.push(x);
+};
+
+/**
+ * @return {number}
+ */
+MyQueue.prototype.pop = function () {
+  if (this.stack.length === 1) {
+    return this.stack.pop();
+  }
+
+  const top = this.stack.pop();
+  const result = this.pop();
+  this.stack.push(top);
+
+  return result;
+};
+
+/**
+ * @return {number}
+ */
+MyQueue.prototype.peek = function () {
+  if (this.stack.length === 1) {
+    return this.stack[this.stack.length - 1];
+  }
+
+  const top = this.stack.pop();
+  const result = this.peek();
+  this.stack.push(top);
+
+  return result;
+};
+
+/**
+ * @return {boolean}
+ */
+MyQueue.prototype.empty = function () {
+  return this.stack.length === 0;
+};
+
+/**
+ * Your MyQueue object will be instantiated and called as such:
+ * var obj = new MyQueue()
+ * obj.push(x)
+ * var param_2 = obj.pop()
+ * var param_3 = obj.peek()
+ * var param_4 = obj.empty()
+ */
diff --git a/sik9252/LinkedListCycle.js b/sik9252/LinkedListCycle.js
new file mode 100644
index 0000000..1055f92
--- /dev/null
+++ b/sik9252/LinkedListCycle.js
@@ -0,0 +1,15 @@
+var hasCycle = function (head) {
+  const visited = new Set();
+  let cur = head;
+
+  while (cur !== null) {
+    if (visited.has(cur)) {
+      return true;
+    }
+
+    visited.add(cur);
+    cur = cur.next;
+  }
+
+  return false;
+};
diff --git a/sik9252/LowestCommonAncestorOfBinarySearchTree.js b/sik9252/LowestCommonAncestorOfBinarySearchTree.js
new file mode 100644
index 0000000..73fba13
--- /dev/null
+++ b/sik9252/LowestCommonAncestorOfBinarySearchTree.js
@@ -0,0 +1,17 @@
+var lowestCommonAncestor = function (root, p, q) {
+  let cur = root;
+  const low = Math.min(p.val, q.val);
+  const high = Math.max(p.val, q.val);
+
+  while (cur !== null) {
+    if (high < cur.val) {
+      cur = cur.left;
+    } else if (low > cur.val) {
+      cur = cur.right;
+    } else {
+      return cur;
+    }
+  }
+
+  return null;
+};