【leetcode】19. 删除链表的倒数第N个节点

//C快慢指针
struct ListNode* removeNthFromEnd(struct ListNode* head, int n) {
    struct ListNode* dummy = malloc(sizeof(struct ListNode));
    dummy->val = 0, dummy->next = head;
    struct ListNode* first = head;
    struct ListNode* second = dummy;
    for (int i = 0; i < n; ++i) {
        first = first->next;
    }
    while (first) {
        first = first->next;
        second = second->next;
    }
    second->next = second->next->next;
    struct ListNode* ans = dummy->next;
    free(dummy);
    return ans;
}

//C递归
struct ListNode* recursion(struct ListNode* head, int* n){
    if(head->next==NULL)
        return head;
    recursion(head->next,n);
    if(--(*n)==0)
        head->next=head->next->next;
    return head->next;
}

struct ListNode* removeNthFromEnd(struct ListNode* head, int n){
    struct ListNode* root=(struct ListNode*)calloc(sizeof(struct ListNode),1);
    root->next=head;
    return recursion(root, &n);
}