题解 | #顺时针旋转矩阵#

先用快慢指针找到中点，然后将后半部分进行翻转，最后在对这两个链表进行合并。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    ListNode* reverse(ListNode* head){
        if(head==NULL||head->next==NULL) return head;
        ListNode* newhead=reverse(head->next);
        head->next->next=head;
        head->next=NULL;
        return newhead;
    }
    void reorderList(ListNode *head) {
        if(head==NULL||head->next==NULL) return ;
        ListNode *fast=head,*slow=head;
        while(fast&&fast->next){
            fast=fast->next->next;
            slow=slow->next;
        }
        ListNode *head2=reverse(slow->next);
        slow->next=NULL;
        ListNode *newhead=new ListNode(0),*p=newhead;
        while(head&&head2){
            p->next=head;
            head=head->next;
            p=p->next;
            p->next=head2;
            head2=head2->next;
            p=p->next;
        }
        if(head) p->next=head;
        if(head2) p->next=head2;
        head=newhead->next;
    }
};