反转一个单链表。

示例:

输入: 1->2->3->4->5->NULL

输出: 5->4->3->2->1->NULL

/**
 * Definition for singly-linked list.
 * public class ListNode {
 *     int val;
 *     ListNode next;
 *     ListNode(int x) { val = x; }
 * }
 */
class Solution {
    public ListNode reverseList(ListNode head) {
        ListNode tempNode = head;
        ListNode pre = null;
        ListNode newHead = null;
        while(tempNode!=null) {
            newHead = new ListNode(tempNode.val);
            newHead.next = pre;
            pre = newHead;
            tempNode = tempNode.next;
        }
        
        return newHead;
    }
}