19. 删除链表的倒数第N个节点

class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        ListNode* dummy = new ListNode(0);
        dummy->next = head;
        ListNode* first = head;
        ListNode* second = dummy;
        while(n--)
        {
            first = first->next;
        }
        while (first!=nullptr) 
        {
            first = first->next;
            second = second->next;
        }
        second->next = second->next->next;
      
        return dummy->next;
    }
};