Palindrome Linked List

public static boolean isPalindrome( ListNode head ) {
    ListNode dummyHead = new ListNode( 0 );
    dummyHead.next = head;
    // 找到链表中点
    ListNode slow = dummyHead, fast = dummyHead;
    while( fast != null && fast.next != null ) {
        slow = slow.next;
        fast = fast.next.next;
    }
    // 翻转中点之后的链表
    ListNode pre = slow, curr = slow.next;
    while( curr != null ) {
        ListNode next = curr.next;
        curr.next = pre;
        pre = curr;
        curr = next;
    }
    // 判断是否回文链表
    ListNode headA = head, headB = pre;
    while( headA != headB ) {
        if( headA.val != headB.val )
            return false;
        headA = headA != headB ? headA.next : headA;
        headB = headB != headA ? headB.next : headB;
    }
    return true;
}