week 7 reverse-linked-list

Author: i-mprovising

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