LeetCode - 234. 回文链表

234. 回文链表

请判断一个链表是否为回文链表。

解题思路： 先用快慢指针找到链表的中间节点，然后将链表断开，将后半段倒序，然后再判断是否为回文。

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode(int x) : val(x), next(NULL) {}
 * };
 */
class Solution {
public:
    bool isPalindrome(ListNode* head) {
        if (!head || !head->next) return true;
        ListNode *fast = head, *slow = head, *pre;
        while (fast && fast->next) {
            fast = fast->next->next;
            pre = slow;
            slow = slow->next;
            // cout << pre->val << endl;
        }
        
        ListNode *t = pre->next;
        pre->next = NULL;
        pre = NULL;
        while (t) {
            ListNode *next = t->next;
            t->next = pre;
            pre = t;
            t = next;
        }
        while (pre && head) {
            if (pre->val != head->val) return false;
            pre = pre->next;
            head = head->next;
        }
        return true;
    }
};