diff --git a/contains-duplicate/reeseo3o.js b/contains-duplicate/reeseo3o.js
new file mode 100644
index 000000000..b9e982549
--- /dev/null
+++ b/contains-duplicate/reeseo3o.js
@@ -0,0 +1,4 @@
+const containsDuplicate = (nums) => {
+  const uniqueCount = new Set(nums).size;
+  return uniqueCount !== nums.length;
+};
diff --git a/top-k-frequent-elements/reeseo3o.js b/top-k-frequent-elements/reeseo3o.js
new file mode 100644
index 000000000..858cd158b
--- /dev/null
+++ b/top-k-frequent-elements/reeseo3o.js
@@ -0,0 +1,27 @@
+const topKFrequent = (nums, k) => {
+    // 1: 등장 횟수 세기
+    const countMap = new Map();
+    for (const num of nums) {
+        countMap.set(num, (countMap.get(num) ?? 0) + 1);
+    }
+
+    // 2: 버킷 배열 만들기
+    // 인덱스 = 빈도수, 값 = 그 빈도수를 가진 숫자들의 배열
+    // 최대 빈도는 nums.length이므로 크기를 nums.length + 1로 설정
+    const bucket = Array.from({ length: nums.length + 1 }, () => []);
+
+    for (const [num, freq] of countMap.entries()) {
+        bucket[freq].push(num);
+    }
+
+    // 3: 뒤(높은 빈도)에서부터 탐색하며 k개 수집
+    const result = [];
+    for (let i = bucket.length - 1; i >= 0 && result.length < k; i--) {
+        for (const num of bucket[i]) {
+            result.push(num);
+            if (result.length === k) break;
+        }
+    }
+
+    return result;
+}
diff --git a/two-sum/reeseo3o.js b/two-sum/reeseo3o.js
new file mode 100644
index 000000000..988ac2e32
--- /dev/null
+++ b/two-sum/reeseo3o.js
@@ -0,0 +1,13 @@
+const twoSum = (nums, target) => {
+  const map = {};
+
+  for (let i = 0; i < nums.length; i++) {
+    const complement = target - nums[i];
+
+    if (complement in map) {
+      return [map[complement], i];
+    }
+
+    map[nums[i]] = i;
+  }
+};