Added solution for problem 0142 linked list cycle 2 in python

python/0142-linked-list-cycle-II.py

@@ -0,0 +1,12 @@
+class Solution(object):
+    def detectCycle(self, head):
+        slow=fast=head
+        while fast and fast.next:
+            slow,fast=slow.next,fast.next.next
+            if slow==fast:
+                break
+        else:
+            return None
+        while head!=slow:
+            head,slow =head.next,slow.next
+        return head