weeok 09 solution linked-list-cycle

Author: HYUNAHKO

linked-list-cycle/HYUNAHKO.py

@@ -0,0 +1,36 @@
+# Definition for singly-linked list.
+# class ListNode:
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+class Solution:
+    def hasCycle(self, head: Optional[ListNode]) -> bool:
+        visited = set()
+
+        current = head
+        while current:
+            if current in visited:
+                return True
+            
+            visited.add(current)
+            current = current.next
+        
+        return False
+
+# w/o set() 
+class Solution:
+    def hasCycle(self, head: Optional[ListNode]) -> bool:
+        if not head or not head.next:
+            return False
+
+        slow = head
+        fast = head.next
+
+        while slow != fast:
+            if not fast or not fast.next:
+                return False
+            slow = slow.next
+            fast = fast.next.next
+
+        return True