c++ 4 liner
\nListNode *slow = head,*fast = head;\n     while(fast && fast->next)\n          slow = slow->next,fast = fast->next->next;\nreturn slow;\n
```\nListNode *slow = head,*fast = head;\n     while(fast && fast->next)\n          slow = slow->next,fast = fast->next->next;\nreturn slow;\n```
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