/**  
 * 判定链表是否是回文  
 *  
 * @param headNode  
 * @author: Max Solider  
 * @date: 2022/10/11 22:39  
 */
 boolean isPalindromeList(NormalListNode headNode) {  
    if (headNode == null || headNode.getNext() == null || headNode.getNext() == headNode) {  
        System.out.println("The linked list is palindrome list.");  
        return true;    }  
    // 先找到中间结点  
    NormalListNode slowPtr = headNode;  
    NormalListNode fastPtr = headNode;  
    while (fastPtr.getNext() != null && fastPtr.getNext().getNext() != null) {  
        fastPtr = fastPtr.getNext().getNext();  
        slowPtr = slowPtr.getNext();  
    }  
    // 逆置后半部分链表  
    NormalListNode secondHalf = reverseList(slowPtr.getNext());  
    NormalListNode firstHalf = headNode;  
    NormalListNode secondHalfHead = secondHalf;  
    boolean palindrome = false;  
    // 因为链表长度可能是奇数，前半部分可能会比后半部分多一个数据，所以用后半部分的长度来遍历  
    while (secondHalf != null) {  
        if (secondHalf.getData() != firstHalf.getData()) {  
            break;  
        }  
        secondHalf = secondHalf.getNext();  
        firstHalf = firstHalf.getNext();  
    }  
    if (palindrome) {  
        System.out.println("The linked list is palindrome list.");  
    } else {  
        System.out.println("The lined list is not palindrome list.");  
    }  
    // 还原后半部分链表  
    reverseList(secondHalfHead);  
    listLength(headNode);  
    return true;}  

/**  
 * 逆置链表  
 *  
 * @author: Max Solider  
 * @date: 2022/10/11 23:26  
 * @param headNode  
 * @return org.example.linkedlist.normal.NormalListNode  
 */
 NormalListNode reverseList(NormalListNode headNode) {  
    if (headNode == null || headNode.getNext() == null) {  
        return headNode;  
    }  
    NormalListNode current = headNode;  
    NormalListNode previous = null;  
    while (current != null) {  
        NormalListNode temp = current.getNext();  
        current.setNext(previous);  
        previous = current;  
        current = temp;  
    }  
    return previous;  
}