Remove Nth Node From End of List

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* removeNthFromEnd(ListNode* head, int n) {
        if(head==NULL&&head->next==NULL)
            return NULL;
        ListNode* newhead=(ListNode*)malloc(sizeof(ListNode));
        newhead->next=head;
        ListNode* pre=newhead;
        ListNode* behind=newhead;
        n++;
        for(int i=0;i<n-1;i++)
            pre=pre->next;
        while(pre->next)
        {
            pre=pre->next;
            behind=behind->next;
        }
        behind->next=behind->next->next;
        return newhead->next;
    }
};