Reorder List

Given a singly linked list L: L0→L1→…→Ln-1→Ln,
reorder it to: L0→Ln→L1→Ln-1→L2→Ln-2→…

You must do this in-place without altering the nodes' values.

#include <iostream>
using namespace std;

struct ListNode {
       int val;
       ListNode *next;
    //ListNode(int x) : val(x), next(NULL) {}
};

class Solution {
public:
    void reorderList(ListNode* head) {
       ListNode* back = head;
       ListNode* tailer;
       int maxPosi=0;
       while(back)
       {
           ++maxPosi;
           tailer = back;
           back = back->next;
       }

       int mid = maxPosi/2;
       ListNode* midlle = head;
       while(mid-- != 0)
       {
           midlle = midlle->next;
       }

       Reverse(midlle);

       ListNode* tmp;
       bool flag = true;

       while(maxPosi-- >1)
       {
              if(flag)
              {
                     tmp = head->next;
                     head->next = tailer;
                     head = tmp;
                     flag = false;
              }
              else
              {
                     tmp = tailer->next;
                     tailer->next = head;
                     tailer = tmp;
                     flag = true;
              }
       }
    }

    ListNode* Reverse(ListNode* head)
    {
        if (!head)
        {
            return NULL;
        }
        ListNode* rtn=NULL;
        ListNode* prev = head;
        ListNode* back = head;
        while(back)
        {
            prev = back;
            back = back->next;

            prev->next = rtn;
            rtn = prev;
        }

        return rtn;
    }
};

int main()
{
    ListNode node[] = {
        {1,node+1},
        {2,node+2},
        {3,node+3},
        {4,node+4},
        {5,node+5},
        {6,node+6},
        {7,NULL}
        };
    ListNode* pNode = node;
    Solution s;
    s.reorderList(node);
    while(pNode)
    {
        cout << pNode->val << endl;
        pNode = pNode->next;
    }
}

从中间位置rever list，然后两端开始一次重新组在一起。