leetcode题解

/**
 * 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 == NULL || head->next == NULL)
            return true;
        ListNode *slow = head, *fast = head;
        while(fast->next != NULL && fast->next->next != NULL){
            slow = slow->next;
            fast = fast->next->next;
        }
        slow->next = reverseList(slow->next);
        slow = slow->next;
        while(slow != NULL){
            if(head->val != slow->val)
                return false;
            head = head->next;
            slow = slow->next;
        }
        return true;
    }
    
    ListNode* reverseList(ListNode *head){
        ListNode *pre = NULL, *next = NULL;
        while(head != NULL){
            next = head->next;
            head->next = pre;
            pre = head;
            head = next;
        }
        return pre;
    }
};