编写一个函数,检查输入的链表是否是回文的。
示例 1:
输入: 1->2
输出: false
示例 2:
输入: 1->2->2->1
输出: true
进阶:
你能否用 O(n) 时间复杂度和 O(1) 空间复杂度解决此题?
来源:力扣(LeetCode) 链接:https://leetcode-cn.com/problems/palindrome-linked-list-lcci 著作权归领扣网络所有。商业转载请联系官方授权,非商业转载请注明出处。
class Solution {
public:
bool isPalindrome(ListNode* head) {
if(!head || !head->next)
return true;
ListNode *halfhead = NULL, *fast = head->next, *slow = head;
while(fast && fast->next)
{
fast = fast->next->next;
slow = slow->next;
}
halfhead = slow->next;
slow->next = NULL;//断开
halfhead = reverseList(halfhead);//反转后半段
while(head && halfhead)//比较
{
if(head->val != halfhead->val)
return false;
head = head->next;
halfhead = halfhead->next;
}
return true;
}
ListNode* reverseList(ListNode *head)
{
ListNode *prev = NULL, *cur = head, *nt = cur->next;
while(cur && cur->next)
{
cur->next = prev;
prev = cur;
cur = nt;
nt = nt->next;
}
cur->next = prev;
return cur;
}
};