/*
public class ListNode {
    int val;
    ListNode next = null;

    ListNode(int val) {
        this.val = val;
    }
}*/
public class Solution {
    public ListNode ReverseList(ListNode head) {
        if(head == null){
            return head;
        }

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