diff --git a/merge-two-sorted-lists/rivkode.py b/merge-two-sorted-lists/rivkode.py
new file mode 100644
index 000000000..6cff0521e
--- /dev/null
+++ b/merge-two-sorted-lists/rivkode.py
@@ -0,0 +1,53 @@
+class ListNode(object):
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+class Solution(object):
+    def mergeTwoLists(self, list1, list2):
+        """
+        :type list1: Optional[ListNode]
+        :type list2: Optional[ListNode]
+        :rtype: Optional[ListNode]
+        """
+        # 더미 노드 생성
+        dummy = ListNode(-1)
+        current = dummy
+
+        # 두 리스트를 순회하며 병합
+        while list1 and list2:
+            if list1.val <= list2.val:
+                current.next = list1
+                list1 = list1.next
+            else:
+                current.next = list2
+                list2 = list2.next
+            current = current.next
+
+        # 남아 있는 노드 처리
+        if list1:
+            current.next = list1
+        elif list2:
+            current.next = list2
+
+        # 더미 노드 다음부터 시작
+        return dummy.next
+
+if __name__ == "__main__":
+    solution = Solution()
+
+    # test case
+    list1 = ListNode(1, ListNode(2, ListNode(4, )))
+    list2 = ListNode(1, ListNode(3, ListNode(4, )))
+
+    result = solution.mergeTwoLists(list1, list2)
+
+    while result is not None:
+        print(result.val)
+        result = result.next
+
+
+
+
+
+
diff --git a/missing-number/rivkode.py b/missing-number/rivkode.py
new file mode 100644
index 000000000..43e1ac29d
--- /dev/null
+++ b/missing-number/rivkode.py
@@ -0,0 +1,38 @@
+class Solution(object):
+    # 시간복잡도 nlog(n) sort
+    # 공간복잡도 n 정렬시
+    def missingNumber_1(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: int
+        """
+        sort_nums = sorted(nums)
+
+        v = 0
+        for i in sort_nums:
+            if v != i:
+                return v
+            else:
+                v += 1
+
+        return v
+
+    # hash를 사용
+    # 모든 숫자를 dict에 입력
+    # for문을 돌면서 해당 hash가 dict에 존재하는지 체크
+    # 시간복잡도 n - for문
+    # 공간복잡도 n - dict 생성
+    def missingNumber(self, nums):
+        hash_keys = dict()
+        for i in range(len(nums) + 1):
+            hash_keys[i] = 0
+        for i in nums:
+            hash_keys[i] = 1
+
+        for i in range(len(nums) + 1):
+            if hash_keys[i] != 1:
+                return i
+
+        return 0
+
+