给定一个链表，请你将链表反转过来。

举例：原链表：1→2→3→4→5→null

         反转链表：5→4→3→2→1→null

代码:

package algorithm_niuke;public class Main {    public static Node reverseList(Node head) {        if(head == null) {            return head;        }                Node pre = null;        Node next = null;                while(head!=null) {            next = head.next;            head.next = pre;            pre = head;            head = next;        }                return pre;    }        private static class Node {        int val;        Node next;                public Node(int val) {            this.val = val;        }    }        public static void main(String[] args) {                    }   }