LeetCode Remove Nth Node From End of List

class Solution {
public:
    ListNode *removeNthFromEnd(ListNode *head, int n) {
        if (head == NULL) return NULL;
        ListNode* pre = NULL;
        ListNode* cur = head;
        ListNode* fast= cur;
        
        for (int i=1; i<n; i++) {
            fast = fast->next;
        }
        
        while (fast->next != NULL) {
            pre = cur;
            cur = cur->next;
            fast= fast->next;
        }
        
        if (pre == NULL) {
            return head->next;
        } else {
            pre->next = cur->next;
            return head;
        }
    }
};