.c

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
 int remov(struct ListNode* current, int n);
 
 int remov(struct ListNode* current, int n){
    if(current==0){
        return 0;
    }
    int count = remov(current->next, n)+1;
    if(count == (n+1) ){
        current->next = current->next->next;
    }
    return count;
}
    
struct ListNode* removeNthFromEnd(struct ListNode* head, int n) {
    int length = remov(head, n);
    return (n==length)? head->next : head;
}