diff --git a/clone-graph/daehyun99.py b/clone-graph/daehyun99.py
new file mode 100644
index 0000000000..197c5c28d3
--- /dev/null
+++ b/clone-graph/daehyun99.py
@@ -0,0 +1,33 @@
+# Time: O(n)
+# Space: 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']:
+        have_to_look = set()
+        seen = set()
+        copied = {}
+
+        have_to_look.add(node)
+
+        while len(have_to_look) > 0 :
+            curr = have_to_look.pop()
+            if curr is not None:
+                if curr.val not in copied:
+                    copied[curr.val] = Node(curr.val, None)
+                for neighbor in curr.neighbors:
+                    if neighbor.val not in copied:
+                        copied[neighbor.val] = Node(neighbor.val, None)
+                        if neighbor.val not in seen:
+                            have_to_look.add(neighbor)
+                    copied[curr.val].neighbors.append(copied[neighbor.val])
+                seen.add(curr.val)
+
+        return copied.get(1, None)
+
diff --git a/longest-repeating-character-replacement/daehyun99.py b/longest-repeating-character-replacement/daehyun99.py
new file mode 100644
index 0000000000..e23a855a5c
--- /dev/null
+++ b/longest-repeating-character-replacement/daehyun99.py
@@ -0,0 +1,59 @@
+# Time: O(s)
+# Space: O(s)
+from collections import defaultdict
+class Solution:
+    def characterReplacement(self, s: str, k: int) -> int:
+        count = defaultdict(int)
+
+        l = 0
+        maxf = 0
+        res = 0
+        for r in range(len(s)):
+            count[s[r]] += 1
+            maxf = max(maxf, count[s[r]])
+
+            while (r - l + 1) - maxf > k:
+                count[s[l]] -= 1
+                l += 1
+            res = max(res, r - l + 1)
+        return res
+
+"""
+# Time: O(s)
+# Space: O(s)
+class Solution:
+    def characterReplacement(self, s: str, k: int) -> int:
+        # find_bunch()
+        bunch = []
+        start_idx = 0
+        start_word = s[0]
+        for i in range(1, len(s)):
+            if s[i] != start_word:
+                bunch.append([start_word, i- start_idx])
+                start_word = s[i]
+                start_idx = i
+        bunch.append([start_word, len(s) - start_idx])
+
+        # find_LRCR()
+        unique = set([c for c in s])
+        result = 0
+
+        for base in unique:
+            changed_num = 0
+            left = 0
+            right = 0
+            length = 0
+            while right < len(bunch):
+                if bunch[right][0] != base:
+                    changed_num += bunch[right][1]
+                length += bunch[right][1]
+                right += 1
+
+                while changed_num > k:
+                    if bunch[left][0] != base:
+                        changed_num -= bunch[left][1]
+                    length -= bunch[left][1]
+                    left += 1
+                result = max(result, min(length + k - changed_num, len(s)))
+        return result
+"""
diff --git a/palindromic-substrings/daehyun99.py b/palindromic-substrings/daehyun99.py
new file mode 100644
index 0000000000..7177202082
--- /dev/null
+++ b/palindromic-substrings/daehyun99.py
@@ -0,0 +1,23 @@
+class Solution:
+    def countSubstrings(self, s: str) -> int:
+        result = 0
+
+        # odd
+        for i in range(0, len(s)):
+            m, n = i, i
+            while 0 <= m and n < len(s) and s[m] == s[n]:
+                result += 1
+                m -= 1
+                n += 1
+
+        # even
+        for i in range(0, len(s)-1):
+            m, n = i, i+1
+            while 0 <= m and n < len(s) and s[m] == s[n]:
+                result += 1
+                m -= 1
+                n += 1
+        return result
+
+
+
diff --git a/reverse-bits/daehyun99.py b/reverse-bits/daehyun99.py
new file mode 100644
index 0000000000..21ef934a10
--- /dev/null
+++ b/reverse-bits/daehyun99.py
@@ -0,0 +1,7 @@
+class Solution:
+    def reverseBits(self, n: int) -> int:
+        res = 0
+        for i in range(32):
+            bit = (n >> i) & 1
+            res += (bit << (31 - i))
+        return res