別想花裡胡哨的了。。倒置刪除再倒置吧，複雜度也就n,就是程式碼長了點

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
   ListNode* removeNthFromEnd(ListNode* head, int n) {
	ListNode *p = head;
 

	ListNode *firstNode = new ListNode(p->val);
	p = p->next;
	ListNode *temp;
	//Reverse
	while (p) {
		temp = new ListNode(p->val);
		temp->next = firstNode;
		firstNode = temp;
		ListNode *d = p;
		p = p->next;
		delete d;
	}
	
	//Remove
	p = firstNode;
	if (n == 1)firstNode = firstNode-
 
>next;
	else
	{
		while (n - 2) {
			--n;
			p = p->next;
		}
		if(p->next->next)p->next = p->next->next;
		else p->next = NULL;
	}
	//Reverse
	p = firstNode;
	if(p)head = new ListNode(p->val);
	else return p;
	p = p->next;
	while (p) {
		temp = new ListNode(p->val);
		temp-
 
>next = head;
		head = temp;
		ListNode* d = p;
		p = p->next;
		delete d;
	}
	return head;
}
};