Leetcode linked list cycle

linked-list.md

@@ -0,0 +1,26 @@
+# Linked list
+
++ [Linked List Cycle](#linked-list-cycle)
+
+## Linked List Cycle
+
+https://leetcode.com/problems/linked-list-cycle/
+
+```python
+# Definition for singly-linked list.
+# class ListNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.next = None
+
+class Solution(object):
+    def hasCycle(self, root):
+        tail = head = root
+        while head and head.next:
+            head = head.next.next
+            tail = tail.next
+            if tail is head:
+                return True
+        return False
+
+```