diff --git a/coin-change/jeldo.py b/coin-change/jeldo.py
new file mode 100644
index 000000000..227a542db
--- /dev/null
+++ b/coin-change/jeldo.py
@@ -0,0 +1,10 @@
+class Solution:
+    # O(n*m), n = len(coins), m = amount
+    def coinChange(self, coins: list[int], amount: int) -> int:
+        dp = [amount+1] * (amount+1)
+        dp[0] = 0
+        for i in range(amount+1):
+            for coin in coins:
+                if i - coin >= 0:
+                    dp[i] = min(dp[i], dp[i-coin]+1)
+        return dp[amount] if dp[amount] != amount+1 else -1
diff --git a/merge-two-sorted-lists/jeldo.py b/merge-two-sorted-lists/jeldo.py
new file mode 100644
index 000000000..371c9ba69
--- /dev/null
+++ b/merge-two-sorted-lists/jeldo.py
@@ -0,0 +1,17 @@
+class Solution:
+    # O(n+m), n = len(list1), m = len(list2)
+    def mergeTwoLists(self, list1: Optional[ListNode], list2: Optional[ListNode]) -> Optional[ListNode]:
+        head = node = ListNode()
+        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
+        if list1:
+            node.next = list1
+        if list2:
+            node.next = list2
+        return head.next
diff --git a/missing-number/jeldo.py b/missing-number/jeldo.py
new file mode 100644
index 000000000..67976636b
--- /dev/null
+++ b/missing-number/jeldo.py
@@ -0,0 +1,5 @@
+class Solution:
+    # O(n), n = len(nums)
+    def missingNumber(self, nums: List[int]) -> int:
+        n = len(nums)
+        return n*(n+1)//2 - sum(nums)
diff --git a/word-search/jeldo.py b/word-search/jeldo.py
new file mode 100644
index 000000000..06e04e833
--- /dev/null
+++ b/word-search/jeldo.py
@@ -0,0 +1,29 @@
+class Solution:
+    # O(m*n), m*n = board's width,heigh
+    def exist(self, board: List[List[str]], word: str) -> bool:
+        dirs = [(0, 1), (1, 0), (0, -1), (-1, 0)]
+        result = False
+
+        def dfs(i, j, visited, w):
+            nonlocal result
+            if (i, j) in visited:
+                return
+            if not (0 <= i < len(board)) or not (0 <= j < len(board[0])):
+                return
+            w += board[i][j]
+            if not (word[:len(w)] == w):
+                return
+            visited.add((i, j))
+            if w == word:
+                result = True
+                return
+            for d in dirs:
+                dfs(i + d[0], j + d[1], visited, w)
+            visited.remove((i, j))  # backtracking
+
+        for i in range(len(board)):
+            for j in range(len(board[0])):
+                dfs(i, j, set(), "")
+                if result:
+                    return True
+        return False