反转链表

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反转链表

递归方法

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   public ListNode reverseList(ListNode head) {
     if(head == null || head.next == null) return head;
        ListNode p = reverseList(head.next);
        head.next.next = head;
        head.next = null;
        return p;
    }
}

循环方法

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public ListNode reverseList(ListNode head) {
      ListNode cur = head, pre = null, next = null;
      while(cur != null){
          next = cur.next;
          cur.next = pre;
          pre = cur;
          cur = next;
      }
      return pre;
  }