[Helena] Week 7

longest-substring-without-repeating-characters/yolophg.py

@@ -0,0 +1,24 @@
+# Time Complexity: O(n): both pointers (left and right) traverse the string once.
+# Space Complexity: O(n): worst case, all characters are unique, so the set will store all characters.
+
+class Solution:
+    def lengthOfLongestSubstring(self, s: str) -> int:
+        # to store characters in the current window
+        window_set = set()  
+        # to store the max length of a substring
+        max_length = 0  
+        # left pointer for the sliding window
+        left = 0  
+
+        # iterate through each char in the string using the right pointer
+        for right in range(len(s)):
+            # if the char is already in the window, shrink the window
+            while s[right] in window_set:
+                window_set.remove(s[left])  # remove the leftmost char
+                left += 1  # move the left pointer to the right
+            # add the new char
+            window_set.add(s[right])
+            # update the max length if the current window is longer
+            max_length = max(max_length, right - left + 1)
+
+        return max_length

reverse-linked-list/yolophg.py

@@ -0,0 +1,14 @@
+# Time Complexity: O(n)
+# Space Complexity: O(1)
+
+class Solution:
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        prev = None
+        # to traverse the original list, starting from head
+        current = head
+        while current:
+            # reverse the link and move to the next node
+            prev, prev.next, current = current, prev, current.next
+
+        # prev is now the head of the reversed list
+        return prev