题解 | #判断一个链表是否为回文结构#

 * struct ListNode {
 *	int val;
 *	struct ListNode *next;
 * };
 */

class Solution {
public:
    /**
     * 
     * @param head ListNode类 the head
     * @return bool布尔型
     */
    ListNode* reverse(ListNode* pHead){
        if(!pHead)
            return NULL;
        ListNode* l=pHead;
        ListNode* r=pHead->next;
        l->next=NULL;
        while(r){
            pHead=r->next;
            r->next=l;
            l=r;
            r=pHead;
        }
        return l;
    }
    bool isPail(ListNode* head) {
        // write code here
        if(!head||!head->next)
            return true;
        ListNode *left,*mid,*right;
        left=head;
        mid=head->next;
        right=head->next->next;
        while(right&&right->next){
            left=left->next;
            mid=mid->next;
            right=right->next->next;
        }
      //  return false;
        if(right){
            left->next=NULL;
            ListNode* cur;
            cur=reverse(mid->next);
            while(head){
                if(head->val!=cur->val)
                    return false;
                head=head->next;
                cur=cur->next;
            }
        }
        else {
            left->next=NULL;
            mid=reverse(mid);
            while(head){
                if(head->val!=mid->val)
                    return false;
                head=head->next;
                mid=mid->next;
            }
        }
        return true;
    }
};