Remove Nth Node From End of List

思路：使用两个指针，其之间距离刚好记录n，这里还是需要注意列表相关题目需要使用头结点或者头指针，这样处理特殊情况会方便很多

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        if(head == nullptr || n == 0)
            return head;
            
        ListNode dummy(-1);
        dummy.next = head;
            
        ListNode *firstNode = &dummy;
        ListNode *secondNode = &dummy;
        
        while(firstNode->next != nullptr)
        {
            if(n<1)
                secondNode = secondNode->next;
            firstNode = firstNode->next;
            --n;
        }
        
        secondNode->next = secondNode->next->next;
        return dummy.next;
    }
};