LeetCode-234. Palindrome Linked List

Given a singly linked list, determine if it is a palindrome.

Example 1:

Input: 1->2
Output: false

Example 2:

Input: 1->2->2->1
Output: true

Follow up:
Could you do it in O(n) time and O(1) space?

题解：

比较主流的解法是找到链表中点，然后翻转后半部分，再判断前半部分和后半部分是否一致。

class Solution {
public:
    bool isPalindrome(ListNode* head) {
        string s, rs;
        ListNode *pre = NULL, *rehead = head;
        while (head != NULL) {
            rehead = head;
            s += to_string(head->val);
            head = head->next;
            rehead->next = pre;
            pre = rehead;
        }
        while (rehead != NULL) {
            rs += to_string(rehead->val);
            rehead = rehead->next;
        }
        return rs == s;
    }
};