diff --git a/contains-duplicate/wooseok123.js b/contains-duplicate/wooseok123.js
new file mode 100644
index 000000000..2d643e052
--- /dev/null
+++ b/contains-duplicate/wooseok123.js
@@ -0,0 +1,7 @@
+// TC : O(n) | SC : O(n)
+
+function containsDuplicate(nums) {
+  let original_length = nums.length;
+  let modified_length = new Set(nums).size;
+  return original_length !== modified_length;
+}
diff --git a/kth-smallest-element-in-a-bst/wooseok123.js b/kth-smallest-element-in-a-bst/wooseok123.js
new file mode 100644
index 000000000..485f0406a
--- /dev/null
+++ b/kth-smallest-element-in-a-bst/wooseok123.js
@@ -0,0 +1,19 @@
+// TC : O(n log n) | SC : O(n)
+
+let findAllValuesInTree = (root, obj) => {
+  obj[root.val] = true;
+  if (!root.left && !root.right) return obj;
+  if (root.left) findAllValuesInTree(root.left, obj);
+  if (root.right) findAllValuesInTree(root.right, obj);
+
+  return obj;
+};
+
+var kthSmallest = function (root, k) {
+  const obj = findAllValuesInTree(root, {});
+  const sortedList = Object.keys(obj)
+    .map(Number)
+    .sort((a, b) => a - b);
+
+  return sortedList[k - 1];
+};
diff --git a/number-of-1-bits/wooseok123.js b/number-of-1-bits/wooseok123.js
new file mode 100644
index 000000000..2d711eb7f
--- /dev/null
+++ b/number-of-1-bits/wooseok123.js
@@ -0,0 +1,34 @@
+let hammingWeight = function (n) {
+  return DecToBinAndGetSetBits(n);
+};
+
+// TC : O(log n) | SC : O(1)
+
+let DecToBinAndGetSetBits = (n) => {
+  let targetNum = n;
+  let result = 0;
+  while (targetNum > 0) {
+    let remainder = targetNum % 2;
+    if (remainder === 1) result += 1;
+    targetNum = parseInt(targetNum / 2);
+  }
+  return result;
+};
+
+// TC : O(log n) | SC : O(log n)
+// 근데 사실 split 메서드 자체는 o(n)인데, toString과정을 통해 log(n)의 개수만큼 나와버린 것이면 o(log n)이라고 표기해도 되는걸까?
+
+// let DecToBinAndGetSetBits = (n) => {
+//     let target = n;
+//     let bin = n.toString(2);
+//     return bin.split("").filter((el) => el == 1).length
+// }
+
+// TC : O(log n) | SC : O(log n)
+
+// let DecToBinAndGetSetBits = (n) => {
+//     let target = n;
+//     let bin = n.toString(2);
+//     let matches = bin.match(/1/g);
+//     return matches.length
+// }
diff --git a/palindromic-substrings/wooseok123.js b/palindromic-substrings/wooseok123.js
new file mode 100644
index 000000000..2f1d47d46
--- /dev/null
+++ b/palindromic-substrings/wooseok123.js
@@ -0,0 +1,24 @@
+var countSubstrings = function (s) {
+  let result = 0;
+  // 개수를 키워나가며, 각 자리가 대칭을 이루는지 검사한다.
+
+  // substring의 개수 설정
+  for (let i = 0; i < s.length; i++) {
+    // 시작점 설정
+    for (let j = 0; j < s.length - i; j++) {
+      let isPalindromic = true;
+      // 대칭되는 요소를 하나씩 비교
+      for (let k = j; k < Math.ceil((j * 2 + i) / 2); k++) {
+        if (s[k] !== s[j * 2 + i - k]) {
+          isPalindromic = false;
+          break;
+        }
+      }
+      if (isPalindromic) result += 1;
+    }
+  }
+
+  return result;
+};
+
+// TC : o(n^3) | SC : o(1)
diff --git a/top-k-frequent-elements/wooseok123.js b/top-k-frequent-elements/wooseok123.js
new file mode 100644
index 000000000..f1e423a59
--- /dev/null
+++ b/top-k-frequent-elements/wooseok123.js
@@ -0,0 +1,15 @@
+// TC : o(n log n) | SC : o(n)
+
+var topKFrequent = function (nums, k) {
+  const elements = countElments(nums);
+  const keys = Object.keys(elements).sort((a, b) => elements[b] - elements[a]);
+  return keys.slice(0, k);
+};
+
+let countElments = (nums) => {
+  const temp = {};
+  for (const num of nums) {
+    temp[num] = (count[num] || 0) + 1;
+  }
+  return temp;
+};