- Reverse Linked List #223

Author: ayosecu

reverse-linked-list/ayosecu.py

@@ -0,0 +1,50 @@
+from typing import Optional
+
+# 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), n = The number of nodes.
+        - Space Complexity: O(1)
+    """
+    def reverseList(self, head: Optional[ListNode]) -> Optional[ListNode]:
+        pre = None
+        while head:
+            nxt = head.next
+            head.next = pre
+            pre = head
+            head = nxt
+        
+        return pre
+
+def toLinkedList(lists):
+    dummy = ListNode(-1)
+    ptr = dummy
+    for item in lists:
+        ptr.next = ListNode(item)
+        ptr = ptr.next
+    return dummy.next
+
+def toList(head):
+    result = []
+    
+    while head:
+        result.append(head.val)
+        head = head.next
+    
+    return result
+
+tc = [
+        ([1, 2, 3, 4, 5], [5, 4, 3, 2, 1]),
+        ([1, 2], [2, 1]),
+        ([], [])
+]
+
+sol = Solution()
+for i, (l, e) in enumerate(tc, 1):
+    r = toList(sol.reverseList(toLinkedList(l)))
+    print(f"TC {i} is Passed!" if r == e else f"TC {i} is Failed! - Expected: {e}, Result: {r}")