Create detect_cycle_II.py

linked_lists/detect_cycle_II.py

@@ -0,0 +1,27 @@
+#!/usr/bin/env python3
+# -*- coding: utf-8 -*-
+# author: bt3gl
+
+
+class ListNode:
+   def __init__(self, x):
+       self.val = x
+       self.next = None
+
+
+def detectCycle(self, head):
+
+        seen = set()
+        node = head
+
+        while node is not None:
+
+            if node in seen:
+                return node
+
+            else:
+                seen.add(node)
+                node = node.next
+
+        return None
+