diff --git a/coin-change/yuseok89.py b/coin-change/yuseok89.py
new file mode 100644
index 0000000000..e4034370cd
--- /dev/null
+++ b/coin-change/yuseok89.py
@@ -0,0 +1,24 @@
+# TC: O(amount * len(coins))
+# SC: O(amount)
+class Solution:
+    def coinChange(self, coins: List[int], amount: int) -> int:
+
+        from collections import deque
+
+        v = {0: 0}
+        q = deque([0])
+
+        while q and amount not in v:
+
+            cur = q.popleft()
+
+            for coin in coins:
+
+                if cur + coin > amount or cur + coin in v:
+                    continue
+
+                v[cur + coin] = v[cur] + 1
+                q.append(cur + coin)
+
+        return -1 if amount not in v else v[amount]
+
diff --git a/find-minimum-in-rotated-sorted-array/yuseok89.py b/find-minimum-in-rotated-sorted-array/yuseok89.py
new file mode 100644
index 0000000000..0ff09b0e55
--- /dev/null
+++ b/find-minimum-in-rotated-sorted-array/yuseok89.py
@@ -0,0 +1,20 @@
+# TC: O(logN)
+# SC: O(1)
+class Solution:
+    def findMin(self, nums: List[int]) -> int:
+        low = 0
+        high = len(nums) - 1
+
+        while low < high - 1:
+            mid = (low + high) // 2
+
+            if nums[low] < nums[mid] < nums[high]:
+                return nums[low]
+
+            if nums[low] > nums[mid]:
+                high = mid
+            else:
+                low = mid
+
+        return min(nums[low], nums[high])
+
diff --git a/maximum-depth-of-binary-tree/yuseok89.py b/maximum-depth-of-binary-tree/yuseok89.py
new file mode 100644
index 0000000000..1ce2f54e8a
--- /dev/null
+++ b/maximum-depth-of-binary-tree/yuseok89.py
@@ -0,0 +1,16 @@
+# TC: O(N)
+# SC: O(H)
+# 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 maxDepth(self, root: Optional[TreeNode]) -> int:
+
+        if not root:
+            return 0
+
+        return max(self.maxDepth(root.left), self.maxDepth(root.right)) + 1
+
diff --git a/merge-two-sorted-lists/yuseok89.py b/merge-two-sorted-lists/yuseok89.py
new file mode 100644
index 0000000000..a461ca9cbf
--- /dev/null
+++ b/merge-two-sorted-lists/yuseok89.py
@@ -0,0 +1,26 @@
+# TC: O(N+M)
+# SC: O(1)
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+class Solution:
+    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
+
+        ret = ListNode()
+        cur = ret
+
+        while list1 and list2:
+            if list1.val < list2.val:
+                cur.next = list1
+                list1 = list1.next
+            else:
+                cur.next = list2
+                list2 = list2.next
+            cur = cur.next
+
+        cur.next = list1 if list1 else list2
+
+        return ret.next
+
diff --git a/word-search/yuseok89.py b/word-search/yuseok89.py
new file mode 100644
index 0000000000..a1ec2bba3e
--- /dev/null
+++ b/word-search/yuseok89.py
@@ -0,0 +1,37 @@
+# TC: O(N*M*4^L)
+# SC: O(L)
+class Solution:
+    def exist(self, board: List[List[str]], word: str) -> bool:
+
+        n = len(board)
+        m = len(board[0])
+
+        board_counter = Counter(board[r][c] for r in range(n) for c in range(m))
+        word_counter = Counter(word)
+
+        for c, cnt in word_counter.items():
+            if board_counter[c] < cnt:
+                return False
+
+        def rec(row, col, idx):
+            if idx == len(word):
+                return True
+
+            if row < 0 or row >= n or col < 0 or col >= m or board[row][col] != word[idx]:
+                return False
+
+            board[row][col] = None
+
+            ret = rec(row + 1, col, idx + 1) or rec(row - 1, col, idx + 1) or rec(row, col + 1, idx + 1) or rec(row, col - 1, idx + 1)
+
+            board[row][col] = word[idx]
+
+            return ret
+
+        for row in range(0, n):
+            for col in range(0, m):
+                if board[row][col] == word[0] and rec(row, col, 0):
+                    return True
+
+        return False
+