Linked List Cycle II

lc142.py

@@ -0,0 +1,28 @@
+# Definition for singly-linked list.
+# class ListNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+
+class Solution(object):
+    def detectCycle(self, head):
+        """
+        :type head: ListNode
+        :rtype: ListNode
+        """
+        if head is None or head.next is None:
+            return None
+        hk = head.next
+        west = hk.next
+        while hk != west:
+            if west is None or west.next is None:
+                return None
+            hk = hk.next
+            west = west.next.next
+
+        hk = head
+        while hk != west:
+            hk = hk.next
+            west = west.next
+        return hk