Java.java

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode() {}
 *     ListNode(int val) { this.val = val; }
 *     ListNode(int val, ListNode next) { this.val = val; this.next = next; }
 * }
 */
class Solution {
    public boolean isPalindrome(ListNode head) {
        
        ListNode fast = head;
        ListNode slow = head;

        //Find the middle
        while(fast != null && fast.next != null){
            fast = fast.next.next;
            slow = slow.next;
        }
        
        //For odd number of Lists, right half should smaller
        if(fast != null){
            slow = slow.next;
        }

        //Reverse the Second Half
        slow = reverseList(slow);
        fast = head;

        //start compare one by one
        while(slow != null){
            if (fast.val != slow.val){
                return false;
            }
            fast = fast.next;
            slow = slow.next;
        }

        return true;

    }

    ListNode reverseList(ListNode head){
        ListNode prev = null;
        ListNode curr = head;
        while(curr != null) {
            ListNode next = curr.next;
            curr.next = prev;
            prev = curr;
            curr = next;
        }
        return prev;
    }
}