Leetcode linked list cycle ii

linked-list.md

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+# Linked list
+
++ [Linked List Cycle II](#linked-list-cycle-ii)
+
+## Linked List Cycle II
+
+https://leetcode.com/problems/linked-list-cycle-ii/
+
+```python
+# 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):
+        tail = curNode = head = _head
+        while curNode and curNode.next:
+            tail = tail.next
+            curNode = curNode.next.next
+            if tail is curNode:
+                break
+        else:
+            return None
+        while head is not tail:
+            tail = tail.next
+            head = head.next
+        return head
+
+```