diff --git a/clone-graph/yuseok89.py b/clone-graph/yuseok89.py
new file mode 100644
index 0000000000..c29a9049fc
--- /dev/null
+++ b/clone-graph/yuseok89.py
@@ -0,0 +1,37 @@
+# TC: O(N)
+# SC: O(N)
+"""
+# Definition for a Node.
+class Node:
+    def __init__(self, val = 0, neighbors = None):
+        self.val = val
+        self.neighbors = neighbors if neighbors is not None else []
+"""
+
+from typing import Optional
+class Solution:
+    def cloneGraph(self, node: Optional['Node']) -> Optional['Node']:
+
+        visited = {}
+
+        def rec(node: Optional['Node']) -> Optional['Node']:
+
+            if not node:
+                return None
+
+            if node.val in visited:
+                return visited[node.val]
+
+            return_val = Node(node.val)
+            visited[node.val] = return_val
+
+            for neighbor in node.neighbors:
+                cloned = rec(neighbor)
+
+                if cloned:
+                    return_val.neighbors.append(cloned)
+
+            return return_val
+
+        return rec(node)
+
diff --git a/longest-common-subsequence/yuseok89.py b/longest-common-subsequence/yuseok89.py
new file mode 100644
index 0000000000..dbe78d900a
--- /dev/null
+++ b/longest-common-subsequence/yuseok89.py
@@ -0,0 +1,22 @@
+# TC: O(N*M)
+# SC: O(M)
+class Solution:
+    def longestCommonSubsequence(self, text1: str, text2: str) -> int:
+
+        n = len(text1)
+        m = len(text2)
+        dp = [[0 for _ in range(m + 1)] for _ in range(2)]
+
+        cur, prev = 1, 0
+
+        for i in range(n):
+            for j in range(m):
+                if text1[i] == text2[j]:
+                    dp[cur][j + 1] = dp[prev][j] + 1
+                else:
+                    dp[cur][j + 1] = max(dp[prev][j + 1], dp[cur][j])
+
+            cur, prev = prev, cur
+
+        return dp[prev][m]
+
diff --git a/longest-repeating-character-replacement/yuseok89.py b/longest-repeating-character-replacement/yuseok89.py
new file mode 100644
index 0000000000..77b82b3cad
--- /dev/null
+++ b/longest-repeating-character-replacement/yuseok89.py
@@ -0,0 +1,27 @@
+# TC: O(N)
+# SC: O(K)
+class Solution:
+    def characterReplacement(self, s: str, k: int) -> int:
+
+        l = 0
+        cnt = defaultdict(int)
+        m, ans = 0, 0
+
+        for r in range(len(s)):
+            c = s[r]
+            cnt[c] += 1
+
+            m = max(m, cnt[c])
+
+            while m + k < r - l + 1:
+                c = s[l]
+                l += 1
+                cnt[c] -= 1
+
+                if cnt[c] == m - 1:
+                    m = max(cnt.values())
+
+            ans = max(ans, r - l + 1);
+
+        return ans
+
diff --git a/palindromic-substrings/yuseok89.py b/palindromic-substrings/yuseok89.py
new file mode 100644
index 0000000000..a5d8ad73d5
--- /dev/null
+++ b/palindromic-substrings/yuseok89.py
@@ -0,0 +1,31 @@
+# TC: O(N^2)
+# SC: O(1)
+class Solution:
+    def countSubstrings(self, s: str) -> int:
+
+        ans = 0
+        n = len(s)
+
+        for center_idx in range(n):
+
+            idx = 0
+
+            while 0 <= center_idx - idx and center_idx + idx < n:
+                if s[center_idx - idx] == s[center_idx + idx]:
+                    ans = ans + 1
+                else:
+                    break
+
+                idx += 1
+
+            idx = 0
+            while 0 <= center_idx - idx and center_idx + idx + 1< n:
+                if s[center_idx - idx] == s[center_idx + idx + 1]:
+                    ans = ans + 1
+                else:
+                    break
+
+                idx += 1
+
+        return ans
+
diff --git a/reverse-bits/yuseok89.py b/reverse-bits/yuseok89.py
new file mode 100644
index 0000000000..c717168ef0
--- /dev/null
+++ b/reverse-bits/yuseok89.py
@@ -0,0 +1,13 @@
+# TC: O(K)
+# SC: O(1)
+class Solution:
+    def reverseBits(self, n: int) -> int:
+        ans = 0
+
+        for _ in range(32):
+            ans *= 2
+            ans += n % 2
+            n //= 2
+
+        return ans
+