lintcode174 删除链表中倒数第n个节点

删除链表中倒数第n个节点

 

给定一个链表，删除链表中倒数第n个节点，返回链表的头节点。

注意事项

链表中的节点个数大于等于n

您在真实的面试中是否遇到过这个题？

Yes

样例

给出链表1->2->3->4->5->null和 n = 2.

删除倒数第二个节点之后，这个链表将变成1->2->3->5->null.

基础：lintcode166 链表倒数第n个节点 

 /**
  * 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
         if (head == NULL || n < ) return NULL;
         ListNode *first = head;
         ListNode *second = head;
         ListNode *pre;
         while (n) {
             first = first->next;
             n--;
         }
         while (first) {
             first = first->next;
             pre = second;  //标记倒数第n个节点的前一个节点
             second = second->next;
         }
         if (second == head) {
             head = head->next;
         } else {
             pre->next = pre->next->next;
         }

         return head;
     }
 };