diff --git a/coin-change/devyejin.py b/coin-change/devyejin.py
new file mode 100644
index 000000000..f725a2fd6
--- /dev/null
+++ b/coin-change/devyejin.py
@@ -0,0 +1,46 @@
+# # 중복조합
+# class Solution:
+#     def coinChange(self, coins: List[int], amount: int) -> int:
+#
+#         def backtrack(current, total):
+#             if total == amount:
+#                 return len(current)
+#
+#             if total > amount:
+#                 return float('inf')
+#
+#             min_count = float('inf')
+#             for coin in coins:
+#                 current.append(coin)
+#                 result = backtrack(current, total + coin)
+#                 min_count = min(min_count, result)
+#                 current.pop()
+#
+#             return min_count
+#
+#         ans = backtrack([], 0)
+#         return -1 if ans == float('inf') else ans
+from collections import deque
+from typing import List
+
+class Solution:
+    def coinChange(self, coins: List[int], amount: int) -> int:
+        if amount == 0:
+            return 0
+
+        queue = deque([(0, 0)])
+        visited = set([0])
+
+        while queue:
+            current_amount, count = queue.popleft()
+
+            for coin in coins:
+                new_amount = current_amount + coin
+                if new_amount == amount:
+                    return count + 1
+                if new_amount < amount and new_amount not in visited:
+                    visited.add(new_amount)
+                    queue.append((new_amount, count + 1))
+
+        return -1
+
diff --git a/find-minimum-in-rotated-sorted-array/devyejin.py b/find-minimum-in-rotated-sorted-array/devyejin.py
new file mode 100644
index 000000000..4ff70cfd4
--- /dev/null
+++ b/find-minimum-in-rotated-sorted-array/devyejin.py
@@ -0,0 +1,3 @@
+class Solution:
+    def findMin(self, nums: List[int]) -> int:
+        return min(nums)
diff --git a/maximum-depth-of-binary-tree/devyejin.py b/maximum-depth-of-binary-tree/devyejin.py
new file mode 100644
index 000000000..7eecbb124
--- /dev/null
+++ b/maximum-depth-of-binary-tree/devyejin.py
@@ -0,0 +1,12 @@
+# 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/maximum-subarray/devyejin.py b/maximum-subarray/devyejin.py
index 1d0ddeb82..b6003864c 100644
--- a/maximum-subarray/devyejin.py
+++ b/maximum-subarray/devyejin.py
@@ -1,10 +1,11 @@
 class Solution:
     def maxSubArray(self, nums: list[int]) -> int:
-        dp = [0] * len(nums)
-        dp[0] = nums[0]
+        current_sum = nums[0]
+        max_sum = nums[0]
 
         for i in range(1, len(nums)):
-            dp[i] = max(nums[i], dp[i - 1] + nums[i])
+            current_sum = max(nums[i], current_sum + nums[i])
+            max_sum = max(current_sum, max_sum)
 
-        return max(dp)
+        return max_sum
 
diff --git a/merge-two-sorted-lists/devyejin.py b/merge-two-sorted-lists/devyejin.py
new file mode 100644
index 000000000..b8e848ec1
--- /dev/null
+++ b/merge-two-sorted-lists/devyejin.py
@@ -0,0 +1,30 @@
+# Definition for singly-linked list.
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+
+"""
+time : O(m+n)
+space : O(1)
+"""
+from typing import Optional
+
+class Solution:
+    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
+        dummy = ListNode()
+
+        node = dummy
+
+        while list1 and list2:
+            if list1.val <= list2.val:
+                node.next = list1
+                list1 = list1.next
+            else:
+                node.next = list2
+                list2 = list2.next
+            node = node.next
+        node.next = list1 or list2
+
+        return dummy.next
diff --git a/word-search/devyejin.py b/word-search/devyejin.py
new file mode 100644
index 000000000..e5f349cdb
--- /dev/null
+++ b/word-search/devyejin.py
@@ -0,0 +1,31 @@
+class Solution:
+    def exist(self, board: list[list[str]], word: str) -> bool:
+        def backtrack(x, y, idx):
+            if idx == len(word):
+                return True
+
+            if not (0 <= x < m and 0 <= y < n) or board[x][y] != word[idx]:
+                return False
+
+            tmp, board[x][y] = board[x][y], "@"
+
+            res = (
+                    backtrack(x + 1, y, idx + 1) or
+                    backtrack(x - 1, y, idx + 1) or
+                    backtrack(x, y + 1, idx + 1) or
+                    backtrack(x, y - 1, idx + 1)
+            )
+
+            board[x][y] = tmp
+            return res
+
+        m = len(board)
+        n = len(board[0])
+
+        for r in range(m):
+            for c in range(n):
+                if backtrack(r, c, 0):
+                    return True
+
+        return False
+