leetcode题目:remove nth node from end of list

class Solution {
public:
    ListNode* (ListNode* head, int n) {
        ListNode *fast = head, *slow = head;
        while(n--)
            fast = fast->next;
        
        if(NULL == fast)
            return head->next;
        fast = fast->next;
        while(fast != NULL){
            fast = fast->next;
            slow = slow->next;
        }
        //删除结点
        slow->next = slow->next->next;
        return head;
    }
};