[doh6077] WEEK 07 solutions

reverse-linked-list/doh6077.py

@@ -0,0 +1,19 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, val=0, next=None):
+#         self.val = val
+#         self.next = next
+# 206. Reverse Linked List
+# 1. Use two pointers 
+# 2. one pointer indicates the current node and another pointer indicate the previous node 
+class Solution:
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        curr = head
+        prev = None
+
+        while curr is not None:
+            nextNode = curr.next
+            curr.next = prev
+            prev = curr 
+            curr = nextNode 
+        return prev