#include<iostream>
#include<vector>
using namespace std;
//Definition for singly-linked list.
/*Given a singly linked list L : L 0→L 1→…→L n - 1→L n,
reorder it to : L 0→L n →L 1→L n - 1→L 2→L n - 2→…*/
struct ListNode {int val;ListNode *next;ListNode(int x) : val(x), next(NULL) {}
};//class Solution {  //没有考虑将最后一个结点删除，并把第二个结点的指针域置为空
//public:           //思路错误
//	void reorderList(ListNode *head) {
//		if (head == NULL || head->next==NULL)
//			return;
//		ListNode *pEnd = head->next;
//		while (pEnd) {
//			pEnd = pEnd->next;
//		}
//		pEnd->next = head->next;
//		head->next = pEnd;
//	}
//};
class Solution {  
public:void reorderList(ListNode *head) {ListNode* p = head;  //保留头结点ListNode *rear = head; while(p!=NULL && p->next!=NULL){ while (rear->next->next!=NULL) {  //找到倒数第二个结点rear = rear->next;}ListNode *temp = rear->next; //保留最后一个结点rear->next = NULL;  //将倒数第二个结点的指针域置为空//插入temp（最后一个结点）将temp插入到p（头结点）和p->next之间temp->next = p->next;p->next = temp;  //将结点插入rear = temp->next;  //保留结点为插入结点的后一个结点p = temp->next;     //将头结点保留为插入结点的后一个结点}}
};//大神思路
class Solution {
public:void reorderList(ListNode *head) {if (!head) return;vector<int> V;ListNode* ptr = head;/*for(; ptr!=NULL; ptr=ptr->next){V.push_back(ptr->val);}*/while (ptr != NULL) {V.push_back(ptr->val);ptr = ptr->next;}int i = 0;int j = V.size() - 1;int flag = 0;ptr = head;while (i <= j) {if ((flag % 2) == 0) {ptr->val = V[i]; i += 1;}else {ptr->val = V[j]; j -= 1;}++flag;ptr = ptr->next;}}
};