给你一个单链表的头节点 head ,请你判断该链表是否为回文链表。如果是,返回 true ;否则,返回 false 。
示例 1:
输入:head = [1,2,2,1]
输出:true
> 代码
class Solution {
public:
bool isPalindrome(ListNode* head) {
if(!head || !head->next)
return 1;
ListNode *fast = head, *slow = head;
ListNode *p, *pre = NULL;
while(fast && fast->next){
p = slow;
slow = slow->next; //快慢遍历
fast = fast->next->next;
p->next = pre; //翻转
pre = p;
}
if(fast) //奇数个节点时跳过中间节点
slow = slow->next;
while(p){ //前半部分和后半部分比较
if(p->val != slow->val)
return 0;
p = p->next;
slow = slow->next;
}
return 1;
}
};