Palindrome Linked List

/**
 * 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:
    int len(ListNode* head){
        if(head==NULL){
            return 0;
        }
        return 1+len(head->next);
    }
    ListNode* reverse(ListNode* head){
        if(head==NULL || head->next==NULL){
            return head;
        }
        ListNode* t=head;
        ListNode* p=reverse(t->next);
        while(t->next!=NULL){
            t=t->next;
        }
        t->next=head;
        head->next=NULL;
        return p;
    }
    bool isPalindrome(ListNode* head) {
        if(head==NULL){
            return true;
        }
        if(head->next==NULL){
            return true;
        }
        ListNode* temp=head;
        int mid=(len(head)+1)/2;
        int i=0;
        while(i<mid-1){
            temp=temp->next;
            i++;
        }
        ListNode* newHead=reverse(temp->next);
        temp->next=NULL;
        while(head!=NULL && newHead!=NULL){
            if(head->val==newHead->val){
                head=head->next;
                newHead=newHead->next;
            }else{
                return false;
            }
        }
        return true;
    }
};