diff --git a/sik9252/BackspaceStringCompare.js b/sik9252/BackspaceStringCompare.js
new file mode 100644
index 0000000..0155252
--- /dev/null
+++ b/sik9252/BackspaceStringCompare.js
@@ -0,0 +1,27 @@
+/**
+ * @param {string} s
+ * @param {string} t
+ * @return {boolean}
+ */
+var backspaceCompare = function (s, t) {
+  const calcS = calc(s);
+  const calcT = calc(t);
+
+  return calcS === calcT;
+};
+
+var calc = function (str) {
+  const stack = [];
+
+  for (let i = 0; i < str.length; i++) {
+    if (!stack.length && str[i] === "#") continue;
+
+    if (str[i] === "#") {
+      stack.pop();
+    } else {
+      stack.push(str[i]);
+    }
+  }
+
+  return [...stack].join("");
+};
diff --git a/sik9252/CountingBits.js b/sik9252/CountingBits.js
new file mode 100644
index 0000000..07510d7
--- /dev/null
+++ b/sik9252/CountingBits.js
@@ -0,0 +1,17 @@
+var countBits = function (n) {
+  const result = [];
+
+  for (let i = 0; i <= n; i++) {
+    let num = i;
+    let count = 0;
+
+    while (num > 0) {
+      num = num & (num - 1);
+      count++;
+    }
+
+    result.push(count);
+  }
+
+  return result;
+};