题解 | #链表的回文结构#

/*
struct ListNode {
    int val;
    struct ListNode *next;
    ListNode(int x) : val(x), next(NULL) {}
};*/
class PalindromeList {
public:
    bool chkPalindrome(ListNode* head) {
        if(head==NULL)return true;
        struct ListNode* slow=head;
        struct ListNode* fast=head;
        while(fast&&fast->next)
        {
            slow=slow->next;
            if(fast->next)
            fast=fast->next->next;
            else
             fast=NULL;
        }
        
        struct ListNode* pre=slow;
        struct ListNode* cur=pre->next;
        struct ListNode* next=cur->next;

        slow->next=slow;
        while(cur)
        {
         cur->next=pre;
         pre=cur;
         cur=next;
        
         if(next)
         next=next->next;
         else
          next=NULL;
        }
        struct ListNode* newhead=head;
        while(pre!=newhead&&pre&&newhead)
        {
            if(pre->val!=newhead->val)
            return false;
            pre=pre->next;
            newhead=newhead->next;
        }
        return true;
    }
};