remove-nth-node-from-end-of-list.c

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     struct ListNode *next;
 * };
 */
struct ListNode* removeNthFromEnd(struct ListNode* head, int n) {
    struct ListNode** p = &head, *q = head;
    for(int i = 0;i < n;i++) {
        q = q->next;
    }
    while(q != NULL) {
        p = &((*p)->next);
        q = q->next;
    }
    *p = (*p)->next;
    return head;
}