check the palindromic list or not

/**
 * Definition for singly-linked list.
 * struct ListNode {
 *     int val;
 *     ListNode *next;
 *     ListNode() : val(0), next(nullptr) {}
 *     ListNode(int x) : val(x), next(nullptr) {}
 *     ListNode(int x, ListNode *next) : val(x), next(next) {}
 * };
 */
class Solution {
public:
    bool isPalindrome(ListNode* head) {
        ListNode* A=head;
         if(!A||!A->next) return true;
        ListNode* slow=A;
    ListNode* fast=A;
    ListNode* back=NULL;
    ListNode* front=A->next;
    while(fast->next!=NULL&&fast->next->next!=NULL)
    {
        fast=fast->next->next;
        back=slow;
        slow=front;
        front=front->next;
        slow->next=back;

    }
     ListNode* left=NULL;
     ListNode* right=NULL;
    if(fast->next==NULL)
    {
        left=slow->next;
        right=front;
    }
    else
    {
        left=slow;
        right=front;
    }
    while(left!=NULL&&right!=NULL)
    {
        if(left->val!=right->val) return false;
        left=left->next;
        right=right->next;
    }
    return true;
    }
};