diff --git a/longest-substring-without-repeating-characters/sun912.py b/longest-substring-without-repeating-characters/sun912.py
new file mode 100644
index 000000000..f89727880
--- /dev/null
+++ b/longest-substring-without-repeating-characters/sun912.py
@@ -0,0 +1,22 @@
+"""
+    TC: O(n)
+    SC: O(n)
+"""
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        str_list = []
+        max_length = 0
+        for i in range(len(s)):
+            if s[i] not in str_list:
+                str_list.append(s[i])
+            else:
+                if max_length < len(str_list):
+                    max_length = len(str_list)
+                str_list = str_list[str_list.index(s[i])+1:]
+                str_list.append(s[i])
+
+        if max_length < len(str_list):
+            max_length = len(str_list)
+
+        return max_length
+
diff --git a/number-of-islands/sun912.py b/number-of-islands/sun912.py
new file mode 100644
index 000000000..b36fbe34b
--- /dev/null
+++ b/number-of-islands/sun912.py
@@ -0,0 +1,26 @@
+"""
+    TC: O(m*n)
+    SC: O(m*n)
+"""
+class Solution:
+    def numIslands(self, grid: List[List[str]]) -> int:
+        def dfs(i, j):
+            if i < 0 or j < 0 or i >= len(grid) or j >= len(grid[0]) or grid[i][j] == "-1" or grid[i][j] == "0":
+                return
+
+            grid[i][j] = "-1"
+            dfs(i+1, j)
+            dfs(i, j+1)
+            dfs(i-1, j)
+            dfs(i, j-1)
+
+        if not grid:
+            return 0
+
+        count = 0
+        for i in range(len(grid)):
+            for j in range(len(grid[0])):
+                if grid[i][j] == "1":
+                    count += 1
+                    dfs(i, j)
+        return count
diff --git a/reverse-linked-list/sun912.py b/reverse-linked-list/sun912.py
new file mode 100644
index 000000000..e28cd18fc
--- /dev/null
+++ b/reverse-linked-list/sun912.py
@@ -0,0 +1,20 @@
+"""
+    TC: O(n)
+    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 reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        node, prev = head, None
+
+        while node:
+            next, node.next = node.next, prev
+            prev, node = node, next
+
+        return prev