O(n) Python solution, slow and fast pointer
\nclass Solution(object):\n    def middleNode(self, head):\n        """\n        :type head: ListNode\n        :rtype: ListNode\n        """\n        slow = hea
```\nclass Solution(object):\n    def middleNode(self, head):\n        """\n        :type head: ListNode\n        :rtype: ListNode\n        """\n        slow = head\n        fast = head\n        while fast and fast.next:\n            slow = slow.next\n            fast = fast.next.next\n            \n        return slow\n```
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