/**  
 * 找到链表倒数第n个结点  
 *  
 * @param headNode  
 * @param n  
 * @return org.example.linkedlist.normal.NormalListNode  
 * @author: Max Solider  
 * @date: 2022/10/9 10:45  
 */
 NormalListNode findNthNodeFromEnd(NormalListNode headNode, int n) {  
    if (headNode == null) {  
        return headNode;  
    }  
    if (n < 1) {  
        System.out.println("The N is invalid. The N must be greater than 0.");  
        return null;    }  
    NormalListNode p1 = headNode, p2 = headNode;  
    int count = 1;  
    while (count != n) {  
        p2 = p2.getNext();  
        if (p2 == null) {  
            System.out.println("The N is invalid. The N must be less than " + (count + 1));  
            return null;        }  
        count++;  
    }  
    while (p2.getNext() != null) {  
        p1 = p1.getNext();  
        p2 = p2.getNext();  
    }  
    System.out.println("倒数第" + n + "个结点的值是：" + p1.getData());  
    return p1;  
}