struct ListNode* removeNthFromEnd(struct ListNode* head, int n){
    if(head->next == NULL)
    {
        return NULL;
    }
    struct ListNode* left = head;
    struct ListNode *p = left;
    while(n -- > 0) {
        left = left ? left->next : NULL;
    }
    if(left == NULL)
    {
        return head->next;
    }
    while(left->next != NULL)
    {
        left = left->next;
        p = p->next;
    }
    p->next = p->next? p->next->next: NULL;
    return head;

}