143. Reorder List

先找到链表中心节点，反转后半段，随后将后半段插入前半段。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    void reorderList(ListNode* head) {
        ListNode *p=head,*q=head;
         if(!q||!q->next)
            return;
        q=q->next;
        q=q->next;
        while(q)
        {
            p=p->next;
            q=q->next;
            if(q==NULL)
            {
                break;
                p=p->next;
            }
            q=q->next;
        }
        ListNode *mid=p;
        
        ListNode*move=mid->next;
        ListNode *end=move;
        int temp=1;
        while(move)
        {
            if(temp)
            {
                temp--;
                move=move->next;
            }
            else
            {
                end->next=move->next;
                
                move->next=mid->next;
                mid->next=move;
                
                move=end->next;
                
            }
        }
        
        ListNode* mov=mid->next; 
        ListNode *link=head;
        mid->next=NULL;
        while(mov)
        {
            ListNode *node=new ListNode(0);
            node->val=mov->val;
            node->next=link->next;
            link->next=node;
            
            mov=mov->next;
            link=node->next;
         
        }
    }
};