/**

 * 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: Nth to last node of a singly linked list.

     */

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

        // write your code here

        if(head==NULL||n==0)

        return NULL;

        ListNode *p1=head;

        ListNode *p2=NULL;

        for(int i=0;i<n-1;i++)

        {

            if(p1->next!=NULL)

            {

                p1=p1->next;

            }

            else

            return NULL;

        }

        p2=head;

        while(p1->next!=NULL)

        {

            p1=p1->next;

            p2=p2->next;

        }

        return p2;

    }

};