/**
 * 反转单链表
 */

/** * 定义链表
 * 
 * @author 16026
 *
 */
class Node {
  int val;
  Node next;
  public Node(int val) {
    this.val = val;
  }
}
public class ReverseList {
  /**
   * 反转链表
   * 
   * @param head
   * @return
   */
  public static Node reverseList(Node head) {
    if (head == null || head.next == null) {
      return head;
    }
    Node reHead = null;// 定义新链表头结点
    while (head != null) {
      Node cur = head.next;// 记录下一个节点
      head.next = reHead;// 将rehead节点连接到head节点上
      reHead = head;// 让rehead指向head
      head = cur;// 将head指向下一个节点
    }
    return reHead;
  }
  /**
   * 递归反转链表
   * 
   * @param head
   * @return
   */
  public static Node reverseList2(Node head) {
    if (head == null || head.next == null)
      return head;
    Node rehead = reverseList2(head.next);
    head.next.next = head;// 将头节点置于末端
    head.next = null;// 防止链表循环
    return rehead;
  }
  /**
   * 打印链表
   * 
   * @param head
   */
  public static void printList(Node head) {
    if (head == null)
      return;
    while (head != null) {
      System.out.print(head.val + " ");
      head = head.next;
    }
  }
  /**
   * 测试
   * 
   * @param args
   */
  public static void main(String[] args) {
    Node n1 = new Node(1);
    Node n2 = new Node(2);
    Node n3 = new Node(3);
    Node n4 = new Node(4);
    Node n5 = new Node(5);
    n1.next = n2;
    n2.next = n3;
    n3.next = n4;
    n4.next = n5;
    // Node rehead = reverseList(n1);
    Node rehead = reverseList2(n1);
    printList(rehead);
  }
}