diff --git a/longest-substring-without-repeating-characters/i-mprovising.py b/longest-substring-without-repeating-characters/i-mprovising.py
new file mode 100644
index 000000000..a3340ec12
--- /dev/null
+++ b/longest-substring-without-repeating-characters/i-mprovising.py
@@ -0,0 +1,37 @@
+from collections import deque
+
+class Solution:
+    """
+    Time complexity O(n)
+    Space complexity O(n)
+    """
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        max_len = 0
+        q = deque()
+        for i, ch in enumerate(s):
+            if ch not in q:
+                q.append(ch)
+                if len(q) > max_len:
+                    max_len = len(q)
+            else:
+                while True:
+                    tmp = q.popleft()
+                    if tmp == ch:
+                        break
+                q.append(ch)
+    
+        return max_len
+    
+    def slidingWindow(self, s):
+        start, end = 0, 0
+        substr = set()
+        max_len = 0
+        while end < len(s):
+            if s[end] in substr:
+                substr.remove(s[start])
+                start += 1
+            else:
+                substr.add(s[end])
+                end += 1
+                max_len = max(end - start, max_len)
+        return max_len
diff --git a/number-of-islands/i-mprovising.py b/number-of-islands/i-mprovising.py
new file mode 100644
index 000000000..29de276f0
--- /dev/null
+++ b/number-of-islands/i-mprovising.py
@@ -0,0 +1,32 @@
+class Solution:
+    """
+    Time, Space comlexity O(n*m)
+    
+    connected components
+    dfs, bfs
+    """
+    def numIslands(self, grid: List[List[str]]) -> int:
+        n, m = len(grid), len(grid[0])
+        visited = [[False for _ in range(m)] for _ in range(n)] # visited 대신 grid를 0으로 표시할수도 있다
+        islands = 0
+    
+        def dfs(x, y):
+            stack = [(x, y)]
+            while stack:
+                x, y = stack.pop()
+                dx = [-1, 1, 0, 0]
+                dy = [0, 0, -1, 1]
+                for k in range(4):
+                    nx, ny = x + dx[k], y + dy[k]
+                    if 0<=nx<=n-1 and 0<=ny<=m-1:
+                        if not visited[nx][ny] and grid[nx][ny] == "1":
+                            visited[nx][ny] = True
+                            stack.append((nx, ny))
+
+        for i in range(n):
+            for j in range(m):
+                if not visited[i][j] and grid[i][j] == "1":
+                    dfs(i, j)
+                    islands += 1
+
+        return islands
diff --git a/reverse-linked-list/i-mprovising.py b/reverse-linked-list/i-mprovising.py
new file mode 100644
index 000000000..d955fb268
--- /dev/null
+++ b/reverse-linked-list/i-mprovising.py
@@ -0,0 +1,25 @@
+# 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)
+    Space complexity O(1)
+    """
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        if not head or not head.next:
+            return head
+
+        node = head.next
+        prev = head
+        prev.next = None
+
+        while node:
+            next_node = node.next
+            node.next = prev
+            prev = node
+            node = next_node
+        
+        return prev
diff --git a/set-matrix-zeroes/i-mprovising.py b/set-matrix-zeroes/i-mprovising.py
new file mode 100644
index 000000000..3a9daf602
--- /dev/null
+++ b/set-matrix-zeroes/i-mprovising.py
@@ -0,0 +1,23 @@
+"""
+Time, space complexity O(m * n)
+"""
+
+class Solution:
+    def setZeroes(self, matrix: List[List[int]]) -> None:
+        """
+        Do not return anything, modify matrix in-place instead.
+        """
+        m, n = len(matrix), len(matrix[0])
+        i_indices = set()
+        j_indices = set()
+        for i in range(m):
+            for j in range(n):
+                if matrix[i][j] == 0:
+                    i_indices.add(i)
+                    j_indices.add(j)
+        
+        for i in i_indices:
+            matrix[i] = [0 for _ in range(n)]
+        for j in j_indices:
+            for i in range(m):
+                matrix[i][j] = 0
diff --git a/unique-paths/i-mprovising.py b/unique-paths/i-mprovising.py
new file mode 100644
index 000000000..1b8d9366f
--- /dev/null
+++ b/unique-paths/i-mprovising.py
@@ -0,0 +1,21 @@
+"""
+Time, space complexity O(m*n)
+
+Dynamic programming
+"""
+
+class Solution:
+    def uniquePaths(self, m: int, n: int) -> int:
+        dp = [[0 for _ in range(n)] for _ in range(m)]
+        dp[0] = [1 for _ in range(n)]
+
+        for i in range(1, m):
+            for j in range(n):
+                if i == 0:
+                    continue
+                if j == 0:
+                    dp[i][j] = 1
+                    continue
+                dp[i][j] = dp[i-1][j] + dp[i][j-1]
+        
+        return dp[-1][-1]