题目：

题解：

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;
}