- Linked List Cycle #225

Author: ayosecu

linked-list-cycle/ayosecu.py

@@ -0,0 +1,53 @@
+from typing import Optional
+
+# Definition for singly-linked list.
+class ListNode:
+    def __init__(self, x):
+        self.val = x
+        self.next = None
+
+class Solution:
+    """
+        - Time Complexity: O(n), n = The number of nodes
+        - Space Complexity: O(1)
+    """
+    def hasCycle(self, head: Optional[ListNode]) -> bool:
+        if not head:
+            return False
+
+        slow, fast = head, head
+        while slow and fast:
+            slow = slow.next
+            if fast.next:
+                fast = fast.next.next
+            else:
+                return False
+
+            if fast == slow:
+                return True
+            
+        return False
+
+# Run Test Cases
+def do_test():
+    sol = Solution()
+
+    h1 = ListNode(3)
+    h1.next = ListNode(2)
+    h1.next.next = ListNode(0)
+    h1.next.next = ListNode(-4)
+    h1.next.next.next = h1.next
+    r1 = sol.hasCycle(h1)
+    print(f"TC 1 is Passed!" if r1 == True else f"TC 1 is Failed!")
+
+    h2 = ListNode(1)
+    h2.next = ListNode(2)
+    h2.next.next = h2
+    r2 = sol.hasCycle(h2)
+    print(f"TC 2 is Passed!" if r2 == True else f"TC 2 is Failed!")
+
+    h3 = ListNode(1)
+    r3 = sol.hasCycle(h3)
+    print(f"TC 3 is Passed!" if r3 == False else f"TC 3 is Failed!")
+
+do_test()