/**

  * Definition of ListNode

  * class ListNode {

  * public:

  *     int val;

  *     ListNode *next;

  *     ListNode(int val) {

  *         this->val = val;

  *         this->next = NULL;

  *     }

  * }

  */

 class Solution {

 public:

     /**

      * @param head: The first node of linked list.

      * @param n: An integer.

      * @return: The head of linked list.

      */

     ListNode *removeNthFromEnd(ListNode *head, int n) {

         // write your code here

         ListNode* pre = head;

         ListNode* cur = head;

         for (int i = ; i < n; i++)

             cur = cur -> next;

         if (!cur) {

             delete pre;

             return pre -> next;

         }

         while (cur -> next) {

             pre = pre -> next;

             cur = cur -> next;

         }

         delete pre -> next;

         pre -> next = pre -> next -> next;

         return head;

     }

 };