Input: 1->2->3->4->5->NULL
Output: 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 cur = head;
        ListNode prev = null;

        while(cur!=null){
            ListNode lat = cur.next;
            cur.next = prev;
            prev = cur;
            cur = lat;
        }
        return prev;

    }    
}