leetcode 之Remove Nth Node From End of List（19）

ListNode *removeNthFromEnd(ListNode *head, int n) {
ListNode dummy{-1, head};
ListNode *p = &dummy, *q = &dummy;
for (int i = 0; i < n; i++) // q 先走 n 步
q = q->next;
while(q->next) { // 一起走
p = p->next;
q = q->next;
}
ListNode *tmp = p->next;
p->next = p->next->next;
delete tmp;
return dummy.next;
}