Simple Ruby solution
\ndef middle_node(head)\n    slow = fast = head\n    while(fast != nil && fast.next != nil)\n        slow = slow.next\n        fast = fast.next.next\n    end\n 
```\ndef middle_node(head)\n    slow = fast = head\n    while(fast != nil && fast.next != nil)\n        slow = slow.next\n        fast = fast.next.next\n    end\n    slow\nend\n```
['Ruby']