diff --git a/climbing-stairs/kayden.py b/climbing-stairs/kayden.py
new file mode 100644
index 000000000..6b1c1ca33
--- /dev/null
+++ b/climbing-stairs/kayden.py
@@ -0,0 +1,12 @@
+# 시간복잡도: O(N)
+# 공간복잡도: O(N)
+class Solution:
+    def climbStairs(self, n: int) -> int:
+        dp = [0] * (n + 1)
+        dp[0] = 1
+        dp[1] = 1
+
+        for i in range(2, n + 1):
+            dp[i] = dp[i - 1] + dp[i - 2]
+
+        return dp[n]
diff --git a/combination-sum/kayden.py b/combination-sum/kayden.py
new file mode 100644
index 000000000..af557cd0b
--- /dev/null
+++ b/combination-sum/kayden.py
@@ -0,0 +1,18 @@
+# 시간복잡도: O(N^M)
+# 공간복잡도: O(M)
+class Solution:
+    def combinationSum(self, candidates: List[int], target: int) -> List[List[int]]:
+        res = []
+
+        def dfs(total, idx, path):
+            if total < 0:
+                return
+            elif total == 0:
+                res.append(path[:])
+
+            for i in range(idx, len(candidates)):
+                dfs(total - candidates[i], i, path + [candidates[i]])
+
+        dfs(target, 0, [])
+
+        return res
diff --git a/encode-and-decode-strings/kayden.py b/encode-and-decode-strings/kayden.py
index 336048beb..d38dbfb8d 100644
--- a/encode-and-decode-strings/kayden.py
+++ b/encode-and-decode-strings/kayden.py
@@ -4,26 +4,30 @@ class Solution:
     # 공간복잡도: O(1)
     def encode(self, strs):
         res = ""
-        for str in strs:
-            size = len(str)
-            res += str(size)
-            res += str
+        for s in strs:
+            size = len(s)
+            res += str(size) + "#" + s  # 문자열 크기와 실제 문자열 사이에 구분자 '#'를 추가
 
         return res
 
     # 시간복잡도: O(N)
     # 공간복잡도: O(N)
-    def decode(self, str):
+    def decode(self, s):
         idx = 0
-        limit = len(str)
+        limit = len(s)
         res = []
 
         while idx < limit:
-            num = str[idx]
-            text = ""
-            for _ in range(num):
-                text += str[idx]
-                idx+=1
+            # 문자열 길이 파싱
+            j = idx
+            while s[j] != '#':  # 구분자 '#'를 찾아 문자열 길이를 추출
+                j += 1
+            num = int(s[idx:j])
+            idx = j + 1  # '#' 다음부터 실제 문자열 시작
+
+            # 실제 문자열 추출
+            text = s[idx:idx + num]
             res.append(text)
+            idx += num
 
         return res
diff --git a/product-of-array-except-self/kayden.py b/product-of-array-except-self/kayden.py
new file mode 100644
index 000000000..44e22a8fb
--- /dev/null
+++ b/product-of-array-except-self/kayden.py
@@ -0,0 +1,18 @@
+# 시간복잡도: O(N)
+# 공간복잡도: out 제외시 O(1)
+class Solution:
+    def productExceptSelf(self, nums: List[int]) -> List[int]:
+        n = len(nums)
+        out = [1] * n
+
+        prod = 1
+        for i in range(n - 1):
+            prod *= nums[i]
+            out[i + 1] *= prod
+
+        prod = 1
+        for i in range(n - 1, 0, -1):
+            prod *= nums[i]
+            out[i - 1] *= prod
+
+        return out
diff --git a/two-sum/kayden.py b/two-sum/kayden.py
new file mode 100644
index 000000000..73630185b
--- /dev/null
+++ b/two-sum/kayden.py
@@ -0,0 +1,21 @@
+# 시간복잡도: O(N)
+# 공간복잡도: O(N)
+class Solution:
+    def twoSum(self, nums: List[int], target: int) -> List[int]:
+        check = {}
+
+        for idx, num in enumerate(nums):
+            check[num] = idx
+
+        for idx, num in enumerate(nums):
+            # 동일한 숫자 두 개가 합쳐져서 목표값이 되는 경우
+            if num * 2 == target:
+                # 그리고 그 숫자가 리스트에 두 개 이상 존재할 경우
+                if check[num] != idx:
+                    return [idx, check[num]]
+                continue
+
+            if target - num in check:
+                return [check[num], check[target - num]]
+
+        return []