struct ListNode {int val;struct ListNode *next;
};
//判断是否链表回文
//比如12321是回文，1221是回文
//1231不是。12323不是
bool isPalindrome(ListNode* pHead){if (pHead == NULL || pHead->next==NULL){//cout<<"if\n";return true;}//计算链表长度//将前半部分反转，然后双指针依次比较int count = 0;ListNode* p = pHead,*q;while(p){p=p->next;count++;}//cout<<"count "<<count<<endl;int i = 0;p = pHead;ListNode *nhead = NULL;while (i < (count/2)){if (nhead==NULL){nhead = p;p = p->next;nhead->next = NULL;}else{q = p;p = p->next;q->next = nhead;nhead = q;}i++;}if (count%2){p=p->next;}while (p){//cout<<p->val<<" "<<nhead->val<<endl;if (p->val != nhead->val){return false;}p=p->next;nhead=nhead->next;}return true;
}
int main(){int s[]={1,2,3,2,7};int i;ListNode *head = NULL;ListNode*p,*q;for (i=0;i<5;i++){p=new ListNode;p->val=s[i];p->next=NULL;if (head==NULL){head=p;q=p;}else{q->next=p;q=p;}}if (isPalindrome(head) == true){cout<<"是回文\n";}else{cout<<"不是回文\n";}while(1);
}