/**

• 反轉連結串列

• 輸入: 1->2->3->4->5->NULL

• 輸出: 5->4->3->2->1->NULL
  */
  class Solution {
  // public static ListNode reverseList(ListNode head) {
  // ListNode prev = null;
  // ListNode cur = head;
  // while(cur != null){
  // ListNode next = cur.next;
  // cur.next = prev;
  // prev = cur;
  // cur = next;
  // }
  // return prev;
  // }
  //遞迴版本
  public static ListNode reverseList(ListNode head){
  if(head == null || head.next == null){
  return head;
  }
  ListNode newHead = reverseList(head.next);
  head.next.next = head;
  head.next = null;
  return newHead;
  }

  public static void main(String[] args) {
  ListNode head = new ListNode(1);
  head.next = new ListNode(2);
  head.next.next = new ListNode(3);
  head.next.next.next = new ListNode(4);
  head.next.next.next.next = new ListNode(5);
  head.next.next.next.next.next = null;
  ListNode result = reverseList(head);
  ListNode p = result;
  while(p != null){
  System.out.print(p.val + "->");
  p = p.next;
  }
  }
  }