diff --git a/clone-graph/kayden.py b/clone-graph/kayden.py
new file mode 100644
index 000000000..500897ca4
--- /dev/null
+++ b/clone-graph/kayden.py
@@ -0,0 +1,28 @@
+from typing import Optional
+from collections import deque
+
+
+class Solution:
+    # 시간복잡도: O(N) node 개수: N
+    # 공간복잡도: O(N)
+    def cloneGraph(self, node: Optional['Node']) -> Optional['Node']:
+        if node:
+            visited = {}
+            copy = Node(val=node.val)
+            visited[copy.val] = copy
+            q = deque()
+            q.append((copy, node))
+
+            while q:
+                cur, node = q.popleft()
+
+                for idx, next_node in enumerate(node.neighbors):
+                    if next_node.val not in visited:
+                        new = Node(val=next_node.val)
+                        visited[new.val] = new
+                        q.append((new, next_node))
+                    cur.neighbors.append(visited[next_node.val])
+
+            return copy
+
+        return node
diff --git a/longest-common-subsequence/kayden.py b/longest-common-subsequence/kayden.py
index d43456d11..c35ac3633 100644
--- a/longest-common-subsequence/kayden.py
+++ b/longest-common-subsequence/kayden.py
@@ -1,17 +1,33 @@
-# 시간복잡도: O(N)
-# 공간복잡도: O(N)
 class Solution:
-    def longestConsecutive(self, nums: List[int]) -> int:
-        nums = set(nums)
-        answer = 0
+    # 시간복잡도: O(A*B)
+    # 공간복잡도: O(A*B)
+    def longestCommonSubsequence(self, text1: str, text2: str) -> int:
+        a = len(text1)
+        b = len(text2)
 
-        for num in nums:
-            if num - 1 not in nums:
-                length = 1
+        lcs = [[0]*(b+1) for _ in range(a+1)]
 
-                while num + length in nums:
-                    length += 1
+        for i in range(1, a+1):
+            for j in range(1, b+1):
+                if text1[i-1] == text2[j-1]:
+                    lcs[i][j] = lcs[i-1][j-1] + 1
+                lcs[i][j] = max(lcs[i][j], lcs[i-1][j], lcs[i][j-1])
 
-                answer = max(answer, length)
+        return lcs[a][b]
 
-        return answer
+    # 시간복잡도: O(A*B)
+    # 공간복잡도: O(A)
+    def longestCommonSubsequence2(self, text1: str, text2: str) -> int:
+        n = len(text1)
+        lcs = [0]*n
+        longest = 0
+        for ch in text2:
+            cur = 0
+            for i in range(n):
+                if cur < lcs[i]:
+                    cur = lcs[i]
+                elif ch == text1[i]:
+                    lcs[i] = cur + 1
+                    longest = max(longest, cur+1)
+
+        return longest
diff --git a/longest-consecutive-sequence/kayden.py b/longest-consecutive-sequence/kayden.py
new file mode 100644
index 000000000..d43456d11
--- /dev/null
+++ b/longest-consecutive-sequence/kayden.py
@@ -0,0 +1,17 @@
+# 시간복잡도: O(N)
+# 공간복잡도: O(N)
+class Solution:
+    def longestConsecutive(self, nums: List[int]) -> int:
+        nums = set(nums)
+        answer = 0
+
+        for num in nums:
+            if num - 1 not in nums:
+                length = 1
+
+                while num + length in nums:
+                    length += 1
+
+                answer = max(answer, length)
+
+        return answer
diff --git a/longest-repeating-character-replacement/kayden.py b/longest-repeating-character-replacement/kayden.py
new file mode 100644
index 000000000..e7cb2397d
--- /dev/null
+++ b/longest-repeating-character-replacement/kayden.py
@@ -0,0 +1,23 @@
+from collections import defaultdict
+
+class Solution:
+    # 시간복잡도: O(N)
+    # 공간복잡도: O(N)
+    def characterReplacement(self, s: str, k: int) -> int:
+
+        n = len(s)
+        l, r = 0, 1
+
+        d = defaultdict(int)
+        d[s[l]] += 1
+
+        longest = 1
+        while l < r and r < n:
+            d[s[r]] += 1
+            if r-l+1 - max(d.values()) > k:
+                d[s[l]] -= 1
+                l += 1
+            longest = max(longest, r-l+1)
+            r += 1
+
+        return longest
diff --git a/merge-two-sorted-lists/kayden.py b/merge-two-sorted-lists/kayden.py
new file mode 100644
index 000000000..ea5ce4b1c
--- /dev/null
+++ b/merge-two-sorted-lists/kayden.py
@@ -0,0 +1,23 @@
+class Solution:
+    # 시간복잡도: O(N+M) list1:N, list2: M
+    # 공간복잡도: O(N+M)
+    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
+        merged = ListNode()
+        cur = merged
+
+        while list1 and list2:
+            if list1.val < list2.val:
+                cur.next = list1
+                list1 = list1.next
+            else:
+                cur.next = list2
+                list2 = list2.next
+            temp = temp.next
+
+        if list1:
+            cur.next = list1
+
+        if list2:
+            cur.next = list2
+
+        return merged.next
diff --git a/sum-of-two-integers/kayden.java b/sum-of-two-integers/kayden.java
new file mode 100644
index 000000000..adc1af9a2
--- /dev/null
+++ b/sum-of-two-integers/kayden.java
@@ -0,0 +1,12 @@
+class Solution {
+    // time: O(1)
+    // space: O(1)
+    public int getSum(int a, int b) {
+        while (b != 0) {
+            int tmp = (a & b) << 1;
+            a = a ^ b;
+            b = tmp;
+        }
+        return a;
+    }
+}