19 Remove Nth Node From End of List

别想花里胡哨的了。。倒置删除再倒置吧，复杂度也就n,就是代码长了点

/**
 * 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;
}
};