234. Palindrome Linked List leetcode

isPalindrome.ts

/**
 * Definition for singly-linked list.
 * class ListNode {
 *     val: number
 *     next: ListNode | null
 *     constructor(val?: number, next?: ListNode | null) {
 *         this.val = (val===undefined ? 0 : val)
 *         this.next = (next===undefined ? null : next)
 *     }
 * }
 */

function isPalindrome(head: ListNode | null): boolean {
    //we nned to rach to mid item  and compare lef and right 
let slow=head;
    let fast=head;
    while(slow && fast && fast.next){
        // push the
        slow=slow.next;
        fast=fast.next.next
        
    }
  fast=head;
    slow=reverse(slow);
    
    while(slow){
   if(slow.val!==fast.val) return false
        slow=slow.next
        fast=fast.next
}

return true
    
    
};

function reverse(head: ListNode | null):ListNode | null{
    let pre=null;
    while(head){
        let temp=head.next;
        head.next=pre;
        pre=head
        head=temp
    }
return pre
    
}