234. Palindrome Linked List

Example 1:

Input: head = [1,2,2,1]
Output: true

Example 2:

Input: head = [1,2]
Output: false

public boolean isPalindrome(ListNode head) {
    ListNode slow = head, fast = head, prev, temp;
    while (fast != null && fast.next != null) {
        slow = slow.next;
        fast = fast.next.next;
    }
    prev = slow;
    slow = slow.next;
    prev.next = null;
    while (slow != null) {
        temp = slow.next;
        slow.next = prev;
        prev = slow;
        slow = temp;
    }
    fast = head;
    slow = prev;
    while (slow != null) {
        if (fast.val != slow.val) return false;
        fast = fast.next;
        slow = slow.next;
    }
    return true;
}