diff --git a/contains-duplicate/doh6077.py b/contains-duplicate/doh6077.py
new file mode 100644
index 000000000..bc14e47f2
--- /dev/null
+++ b/contains-duplicate/doh6077.py
@@ -0,0 +1,10 @@
+
+# set에 저장하면서 중복 여부 확인하기
+class Solution:
+    def containsDuplicate(self, nums: list[int]) -> bool:
+        hashset = set()
+        for i in nums:
+            if i in hashset:
+                return True
+            hashset.add(i)
+        return False
diff --git a/longest-consecutive-sequence/doh6077.py b/longest-consecutive-sequence/doh6077.py
new file mode 100644
index 000000000..75df1d3fe
--- /dev/null
+++ b/longest-consecutive-sequence/doh6077.py
@@ -0,0 +1,34 @@
+# 배열을 정렬하고 포인터를 두개 사용
+class Solution:
+    def longestConsecutive(self, nums: List[int]) -> int:
+        if not nums:
+            return 0
+        
+        # sort the given list 
+        sorted_nums = sorted(nums)
+    
+        longest = 1
+        curr = 1
+        
+        l, r = 0, 1
+        
+        while r < len(sorted_nums):
+            # case 1: exactly consecutive (x, x+1)
+            if sorted_nums[r] == sorted_nums[l] + 1:
+                curr += 1
+                longest = max(longest, curr)
+                l += 1
+                r += 1
+            
+            # case 2: duplicate (x, x) → ignore, move right pointer
+            elif sorted_nums[r] == sorted_nums[l]:
+                l += 1
+                r += 1
+            
+            # case 3: gap
+            else:
+                curr = 1
+                l = r
+                r += 1
+        
+        return longest
diff --git a/two-sum/doh6077.py b/two-sum/doh6077.py
new file mode 100644
index 000000000..2054ef0de
--- /dev/null
+++ b/two-sum/doh6077.py
@@ -0,0 +1,8 @@
+class Solution:
+    def twoSum(self, nums: list[int], target: int) -> list[int]:
+        prevMap = {} # val : index 
+        for i, n in enumerate(nums):
+            diff = target - n 
+            if diff in prevMap:
+                return [prevMap[diff], i]
+            prevMap[n] = i