题目：

题解：

class Solution {
public:ListNode* removeNthFromEnd(ListNode* head, int n) {ListNode* dummy = new ListNode(0, head);ListNode* first = head;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;ListNode* ans = dummy->next;delete dummy;return ans;}
};