/**

 * Definition for singly-linked list.

 * struct ListNode {

 *     int val;

 *     ListNode *next;

 *     ListNode(int x) : val(x), next(NULL) {}

 * };

 */

 /*

 求长度

 找前驱

 删除

 */

class Solution {

public:

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

        int len = ;

        ListNode* p = head;

        while(p){

            len++;

            p=p->next;

        }

        p = head;

        ListNode* pre = NULL;

        int m = len -n;

        while(m){

            pre = p;

            p=p->next;

            m--;

        }

        if(pre){

            pre->next = p->next;

        }else{

            p = head;

            head = head->next;

        }

        delete(p);

        return head;

    }

};