diff --git a/contains-duplicate/daehyun99.py b/contains-duplicate/daehyun99.py
new file mode 100644
index 0000000000..44b3d7c2e9
--- /dev/null
+++ b/contains-duplicate/daehyun99.py
@@ -0,0 +1,10 @@
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        seen = set()
+        
+        for num in nums:
+            if num in seen:
+                return True
+            else:
+                seen.add(num)
+        return False
diff --git a/top-k-frequent-elements/daehyun99.py b/top-k-frequent-elements/daehyun99.py
new file mode 100644
index 0000000000..5aca3e1a1f
--- /dev/null
+++ b/top-k-frequent-elements/daehyun99.py
@@ -0,0 +1,22 @@
+# Time: O(nk)
+# Space: O(n)
+from collections import defaultdict
+
+class Solution:
+    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+        nums_dict = defaultdict(int)
+
+        for num in nums:
+            nums_dict[num] += 1
+
+        result = []
+        for i in range(k):
+            max_count = 0
+            max_num = 0
+            for num, count in nums_dict.items():
+                if max_count < count:
+                    max_count = count
+                    max_num = num
+            nums_dict[max_num] = 0
+            result.append(max_num)
+        return result
diff --git a/two-sum/daehyun99.py b/two-sum/daehyun99.py
new file mode 100644
index 0000000000..8385da2f7f
--- /dev/null
+++ b/two-sum/daehyun99.py
@@ -0,0 +1,24 @@
+# Time: O(n)
+# Space: O(2n)
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        set_nums = set(nums)
+        for j in range(len(nums)-1, -1, -1):
+            val = target - nums[j]
+            if val in set_nums:
+                i = nums.index(val)
+                if i != j:
+                    return [i, j]
+
+"""
+# Time: O(n^2)
+# Space: O(1)
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        for i in range(len(nums)-1):
+            for j in range(i+1, len(nums)):
+                if nums[i] + nums[j] == target:
+                    return [i, j]
+
+
+"""