diff --git a/coin-change/ayosecu.py b/coin-change/ayosecu.py
new file mode 100644
index 000000000..2c9c37132
--- /dev/null
+++ b/coin-change/ayosecu.py
@@ -0,0 +1,30 @@
+from typing import List
+
+class Solution:
+    """
+        - Time Complexity: O(CA), C = len(coins), A = amount
+        - Space Complexity: O(A), A = amount
+    """
+    def coinChange(self, coins: List[int], amount: int) -> int:
+        # DP
+        dp = [float("inf")] * (amount + 1)
+        dp[0] = 0   # 0 amount needs 0 coin
+
+        for coin in coins:
+            for i in range(coin, amount + 1):
+                # dp[i] => not use current coin
+                # dp[i - coin] + 1 => use current coin
+                dp[i] = min(dp[i], dp[i - coin] + 1)
+        
+        return dp[amount] if dp[amount] != float("inf") else -1
+
+tc = [
+        ([1,2,5], 11, 3),
+        ([2], 3, -1),
+        ([1], 0, 0)
+]
+
+for i, (coins, amount, e) in enumerate(tc, 1):
+    sol = Solution()
+    r = sol.coinChange(coins, amount)
+    print(f"TC {i} is Passed!" if r == e else f"TC {i} is Failed! - Expected: {e}, Result: {r}")
diff --git a/find-minimum-in-rotated-sorted-array/ayosecu.py b/find-minimum-in-rotated-sorted-array/ayosecu.py
new file mode 100644
index 000000000..063228b7a
--- /dev/null
+++ b/find-minimum-in-rotated-sorted-array/ayosecu.py
@@ -0,0 +1,32 @@
+from typing import List
+
+class Solution:
+    """
+        - Time Complexity: O(logn), n = len(nums)
+        - Space Complexity: O(1)
+    """
+    def findMin(self, nums: List[int]) -> int:
+        # Binary Search
+        l, r = 0, len(nums) - 1
+
+        while l < r:
+            mid = (l + r) // 2            
+            if nums[mid] > nums[r]:
+                # if min number located in right side
+                l = mid + 1
+            else:
+                # if min number located in left side (including current pivot)
+                r = mid
+        
+        return nums[l]
+
+tc = [
+        ([3,4,5,1,2], 1),
+        ([4,5,6,7,0,1,2], 0),
+        ([11,13,15,17], 11)
+]
+
+for i, (nums, e) in enumerate(tc, 1):
+    sol = Solution()
+    r = sol.findMin(nums)
+    print(f"TC {i} is Passed!" if r == e else f"TC {i} is Failed! - Expected: {e}, Result: {r}")
diff --git a/maximum-depth-of-binary-tree/ayosecu.py b/maximum-depth-of-binary-tree/ayosecu.py
new file mode 100644
index 000000000..e5dc56766
--- /dev/null
+++ b/maximum-depth-of-binary-tree/ayosecu.py
@@ -0,0 +1,53 @@
+from typing import Optional
+
+# 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:
+    """
+        - Time Complexity: O(n), n = The number of nodes in tree
+        - Space Complexity: O(H), H = The height of tree,
+            - H = logn, if the tree is balanced
+            - H = n, if the tree is skewed
+    """
+    def maxDepth(self, root: Optional[TreeNode]) -> int:
+        if not root:
+            return 0
+        
+        # dfs : count the depth
+        max_depth = 0
+        
+        def dfs(node, count):
+            nonlocal max_depth
+            
+            if not node:
+                max_depth = max(max_depth, count)
+                return
+            
+            dfs(node.left, count + 1)
+            dfs(node.right, count + 1)
+            
+        dfs(root, 0)
+        
+        return max_depth        
+
+def doTest():
+    sol = Solution()
+
+    root1 = TreeNode(3)
+    root1.left = TreeNode(9)
+    root1.right = TreeNode(20)
+    root1.right.left = TreeNode(15)
+    root1.right.right = TreeNode(7)
+    print("TC 1 is Success!" if sol.maxDepth(root1) == 3 else "TC 1 is Failed!")
+
+    root2 = TreeNode(1)
+    root2.right = TreeNode(2)
+    print(f"TC 2 is Success!" if sol.maxDepth(root2) == 2 else "TC 2 is Failed!")
+
+    print(f"TC 3 is Success!" if sol.maxDepth(None) == 0 else "TC 3 is Failed!")
+doTest()
diff --git a/merge-two-sorted-lists/ayosecu.py b/merge-two-sorted-lists/ayosecu.py
new file mode 100644
index 000000000..7b9c6492d
--- /dev/null
+++ b/merge-two-sorted-lists/ayosecu.py
@@ -0,0 +1,62 @@
+from typing import Optional
+
+# Definition for singly-linked list.
+class ListNode:
+    def __init__(self, val=0, next=None):
+        self.val = val
+        self.next = next
+
+class Solution:
+    """
+        - Time Complexity: O(n + m), n = len(list1), m = len(list2)
+        - Space Complexity: O(1)
+    """
+    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
+        # two pointers
+        p1, p2 = list1, list2
+        dummy = ListNode(0)
+        current = dummy
+        
+        while p1 and p2:  
+            if p1.val < p2.val:
+                current.next = p1
+                p1 = p1.next
+            else:
+                current.next = p2
+                p2 = p2.next
+            current = current.next
+        
+        current.next = p1 if p1 else p2
+        
+        return dummy.next
+
+def printList(list):
+    if not list:
+        print("[]")
+        return
+    
+    str_list = []
+    while list:
+        str_list.append(str(list.val))
+        list = list.next
+    print("[" + ", ".join(str_list) + "]")
+
+def doTest():
+    sol = Solution()
+
+    list1 = ListNode(1)
+    list1.next = ListNode(2)
+    list1.next.next = ListNode(4)
+    list2 = ListNode(1)
+    list2.next = ListNode(3)
+    list2.next.next = ListNode(4)
+    result1 = sol.mergeTwoLists(list1, list2)
+    printList(result1)
+
+    result2 = sol.mergeTwoLists(None, None)
+    printList(result2)
+
+    result3 = sol.mergeTwoLists(None, ListNode(0))
+    printList(result3)
+
+doTest()
diff --git a/word-search/ayosecu.py b/word-search/ayosecu.py
new file mode 100644
index 000000000..257a3693b
--- /dev/null
+++ b/word-search/ayosecu.py
@@ -0,0 +1,52 @@
+from typing import List
+
+class Solution:
+    """
+        - Time Complexity: O(m*n*3^w)
+            - m = len(board), n = len(board[0]), w = len(word)
+            - m * n => finding start point
+            - 3^w => There are three ways for visiting recursively until find a word
+        - Space Complexity: O(w)
+            - The sum of stack's space => The depth of dfs => len(word)
+    """
+    def exist(self, board: List[List[str]], word: str) -> bool:
+        m, n = len(board), len(board[0])
+        
+        # DFS approach
+        def dfs(i, j, leng):
+            if leng == len(word):
+                # Found!
+                return True
+            
+            if not (0 <= i < m and 0 <= j < n) or board[i][j] != word[leng]:
+                # Wrong position or Not matched
+                return False
+
+            temp = board[i][j]  # Backup
+            board[i][j] = "#"   # Visited
+            for dx, dy in [(1, 0), (0, 1), (-1, 0), (0, -1)]:
+                if dfs(i + dx, j + dy, leng + 1):
+                    return True
+            board[i][j] = temp  # Restore
+
+            return False
+        
+        # Finding Start Point
+        for i in range(m):
+            for j in range(n):
+                if word[0] == board[i][j]:
+                    if dfs(i, j, 0):
+                        return True
+    
+        return False
+
+tc = [
+        ([["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], "ABCCED", True),
+        ([["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], "SEE", True),
+        ([["A","B","C","E"],["S","F","C","S"],["A","D","E","E"]], "ABCB", False)
+]
+
+for i, (board, word, e) in enumerate(tc, 1):
+    sol = Solution()
+    r = sol.exist(board, word)
+    print(f"TC {i} is Passed!" if r == e else f"TC {i} is Failed! - Expected: {e}, Result: {r}")