leetcode

 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class  {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        if(n == 0) return head;
        if(head == NULL) return head;
        ListNode *pl = head, *pr = head;
        for(int i = 1; i <= n; ++i) pr = pr->next;
        if(pr == NULL) {
            head = head->next;
            return head;
        }
        while(pr->next != NULL){
            pr = pr->next;
            pl = pl->next;
        }
        pl->next = pl->next->next;
        return head;
    }
};