leetcode 234 回文链表

题目

请判断一个链表是否为回文链表。

 

解题思路

反转链表的后半段。

 

C++代码

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