diff --git a/contains-duplicate/o-ddong.py b/contains-duplicate/o-ddong.py
new file mode 100644
index 000000000..0648d87c5
--- /dev/null
+++ b/contains-duplicate/o-ddong.py
@@ -0,0 +1,3 @@
+class Solution:
+    def containsDuplicate(self, nums: List[int]) -> bool:
+        return len(nums) != len(set(nums))
diff --git a/house-robber/o-ddong.py b/house-robber/o-ddong.py
new file mode 100644
index 000000000..bda3c8b68
--- /dev/null
+++ b/house-robber/o-ddong.py
@@ -0,0 +1,15 @@
+class Solution:
+    def rob(self, nums: List[int]) -> int:
+        if not nums:
+            return 0
+        elif len(nums) == 1:
+            return nums[0]
+        
+        dp = [0] * len(nums)
+        dp[0] = nums[0]
+        dp[1] = max(nums[0], nums[1])
+
+        for idx in range(2, len(nums)):
+            dp[idx] = max(nums[idx-1], nums[idx] + nums[idx-2])
+
+        return dp[-1]
diff --git a/longest-consecutive-sequence/o-ddong.py b/longest-consecutive-sequence/o-ddong.py
new file mode 100644
index 000000000..dfafc50d1
--- /dev/null
+++ b/longest-consecutive-sequence/o-ddong.py
@@ -0,0 +1,17 @@
+class Solution:
+    def longestConsecutive(self, nums: List[int]) -> int:
+        if not nums:
+            return 0
+
+        nums = sorted(set(nums))
+        longest_streak = 1
+        current_streak = 1
+
+        for i in range(1, len(nums)):
+            if nums[i] == nums[i - 1] + 1:
+                current_streak += 1
+            else:
+                longest_streak = max(longest_streak, current_streak)
+                current_streak = 1
+
+        return max(longest_streak, current_streak)
diff --git a/top-k-frequent-elements/o-ddong.py b/top-k-frequent-elements/o-ddong.py
new file mode 100644
index 000000000..27a4d252e
--- /dev/null
+++ b/top-k-frequent-elements/o-ddong.py
@@ -0,0 +1,5 @@
+import collections
+
+class Solution:
+    def topKFrequent(self, nums: List[int], k: int) -> List[int]:
+        return [num for num, cnt in collections.Counter(nums).most_common(k)]
diff --git a/valid-palindrome/o-ddong.py b/valid-palindrome/o-ddong.py
new file mode 100644
index 000000000..0c27faa7b
--- /dev/null
+++ b/valid-palindrome/o-ddong.py
@@ -0,0 +1,10 @@
+import re
+
+class Solution:
+    def isPalindrome(self, s: str) -> bool:
+        filtered_phrase = re.sub("[^a-zA-Z0-9]", "", s).lower()
+
+        if filtered_phrase == filtered_phrase[::-1]:
+            return True
+        else:
+            return False