diff --git a/longest-palindromic-substring/Chaedie.py b/longest-palindromic-substring/Chaedie.py
new file mode 100644
index 000000000..984ae8219
--- /dev/null
+++ b/longest-palindromic-substring/Chaedie.py
@@ -0,0 +1,40 @@
+"""
+Solution: 
+    1) 포문을 돌면서 좌우 투포인터로 벌려주며 같은 문자인지 확인한다. 같으면 팰린드롬, 아니면 break
+    2) 홀수, 짝수를 별도로 순회한다.
+
+Time: O(n^2)
+Space: O(1)
+"""
+
+class Solution:
+    def longestPalindrome(self, s: str) -> str:
+        result = s[0]
+
+        for i in range(len(s)):
+            # check odd
+            word = s[i]
+            left, right = i - 1, i + 1
+            while left >= 0 and right < len(s):
+                if s[left] == s[right]:
+                    word = s[left] + word + s[right]
+                    if len(result) < len(word):
+                        result = word
+                    left -= 1
+                    right += 1
+                else: 
+                    break
+
+            word = ""
+            left, right = i, i + 1
+            while left >= 0 and right < len(s):
+                if s[left] == s[right]:
+                    word = s[left] + word + s[right]
+                    if len(result) < len(word):
+                        result = word
+                    left -= 1
+                    right += 1
+                else: 
+                    break
+
+        return result
diff --git a/rotate-image/Chaedie.py b/rotate-image/Chaedie.py
new file mode 100644
index 000000000..4ca5e706a
--- /dev/null
+++ b/rotate-image/Chaedie.py
@@ -0,0 +1,32 @@
+"""
+Solution: 1) 가장 바깥에서부터 안쪽으로 들어오며 4 원소의 자리를 바꿔준다.
+Time: O(n^2)
+Space: O(1)
+"""
+
+
+class Solution:
+    def rotate(self, matrix: List[List[int]]) -> None:
+        ROWS, COLS = len(matrix), len(matrix[0])
+
+
+        l, r = 0, COLS - 1
+        t, b = 0, ROWS - 1
+        while l < r and t < b:
+            for i in range(r - l):
+                [
+                    matrix[t][l + i], 
+                    matrix[t + i][r], 
+                    matrix[b][r - i], 
+                    matrix[b - i][l]
+                ] = [
+                    matrix[b - i][l], 
+                    matrix[t][l + i], 
+                    matrix[t + i][r],
+                    matrix[b][r - i]
+                ]
+
+            l += 1
+            r -= 1
+            t += 1
+            b -= 1
diff --git a/subtree-of-another-tree/Chaedie.py b/subtree-of-another-tree/Chaedie.py
new file mode 100644
index 000000000..e3d4afd9c
--- /dev/null
+++ b/subtree-of-another-tree/Chaedie.py
@@ -0,0 +1,25 @@
+# Definition for a binary tree node.
+# class TreeNode:
+#     def __init__(self, val=0, left=None, right=None):
+#         self.val = val
+#         self.left = left
+#         self.right = right
+class Solution:
+    def isSubtree(self, root: Optional[TreeNode], subRoot: Optional[TreeNode]) -> bool:
+        if not subRoot: return True
+        if not root: return False
+        
+        if self.sameTree(root, subRoot):
+            return True
+
+        return (self.isSubtree(root.left, subRoot) or 
+                self.isSubtree(root.right, subRoot))
+
+    def sameTree(self, s, t):
+        if not s and not t:
+            return True
+        
+        if s and t and s.val == t.val:
+            return (self.sameTree(s.left, t.left) and
+                    self.sameTree(s.right, t.right))
+        return False