diff --git a/contains-duplicate/hwanminini.js b/contains-duplicate/hwanminini.js
new file mode 100644
index 000000000..efe53211a
--- /dev/null
+++ b/contains-duplicate/hwanminini.js
@@ -0,0 +1,10 @@
+// 시간복잡도: O(n)
+// 공간복잡도: O(n)
+
+/**
+ * @param {number[]} nums
+ * @return {boolean}
+ */
+var containsDuplicate = function(nums) {
+    return nums.length !== new Set(nums).size
+};
diff --git a/kth-smallest-element-in-a-bst/hwanminini.js b/kth-smallest-element-in-a-bst/hwanminini.js
new file mode 100644
index 000000000..1c9b30500
--- /dev/null
+++ b/kth-smallest-element-in-a-bst/hwanminini.js
@@ -0,0 +1,31 @@
+// 시간 복잡도: O(n log n)
+// 공간 복잡도: O(n)
+
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @param {number} k
+ * @return {number}
+ */
+var kthSmallest = function(root, k) {
+    const results = []
+
+    const dfs = (tree) => {
+        results.push(tree.val)
+        if (tree.left) dfs(tree.left)
+        if (tree.right) dfs(tree.right)
+    }
+
+    dfs(root)
+
+    results.sort((a,b) => a - b)
+
+    return results[k-1]
+};
diff --git a/number-of-1-bits/hwanmini.js b/number-of-1-bits/hwanmini.js
new file mode 100644
index 000000000..dca0de297
--- /dev/null
+++ b/number-of-1-bits/hwanmini.js
@@ -0,0 +1,20 @@
+// 시간복잡도: O(log n)
+// 공간복잡도: O(log n)
+
+const replaceZeroToEmptyString = (str) => str.replaceAll('0','')
+
+
+/**
+ * @param {number} n
+ * @return {number}
+ */
+var hammingWeight = function(n) {
+    const binaryNum = n.toString(2)
+    const replacedNumber = replaceZeroToEmptyString(binaryNum)
+    return replacedNumber.length
+};
+
+
+console.log(hammingWeight(11));
+console.log(hammingWeight(128));
+console.log(hammingWeight(2147483645));
diff --git a/palindromic-substrings/hwanminini.js b/palindromic-substrings/hwanminini.js
new file mode 100644
index 000000000..53c4eb979
--- /dev/null
+++ b/palindromic-substrings/hwanminini.js
@@ -0,0 +1,35 @@
+// 시간 복잡도: O(n^3)
+// 공간 복잡도: O(1)
+
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var countSubstrings = function(s) {
+    let count = 0;
+
+    let plusIndex = 0;
+    while (plusIndex !== s.length) {
+        for (let i = 0 ; i < s.length - plusIndex; i++) {
+            if (isValidSubstring(s, i, i + plusIndex)) count++
+        }
+
+        plusIndex++;
+    }
+
+    return count;
+};
+
+
+function isValidSubstring(s, left, right) {
+    while (left <= right) {
+        if (s[left] !== s[right]) return false;
+
+        left++;
+        right--;
+    }
+    return true;
+}
+
+console.log(countSubstrings("abc"));
+console.log(countSubstrings("aaa"));
diff --git a/top-k-frequent-elements/hwanmini.js b/top-k-frequent-elements/hwanmini.js
new file mode 100644
index 000000000..2509f3c6d
--- /dev/null
+++ b/top-k-frequent-elements/hwanmini.js
@@ -0,0 +1,30 @@
+// 시간복잡도: O(n)
+// 공간복잡도: O(n)
+
+/**
+ * @param {number[]} nums
+ * @param {number} k
+ * @return {number[]}
+ */
+var topKFrequent = function(nums, k) {
+    const map = new Map()
+
+    for (let i = 0; i < nums.length; i++) {
+        map.set(nums[i], (map.get(nums[i]) || 0) + 1);
+    }
+
+    const buckets = Array.from({length: nums.length + 1}, () => [])
+
+    for (const [num, frequency] of map.entries()) {
+        buckets[frequency].push(num);
+    }
+
+    const result = [];
+    for (let i = buckets.length - 1; i >= 0 && result.length < k; i--) {
+        result.push(...buckets[i]);
+    }
+
+    return result
+};
+
+console.log(topKFrequent([1,1,1,2,2,3],2))