/*
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;
        ListNode curr = head;
        while(curr != null){
            ListNode next = curr.next ;
            curr.next = prev;
            prev = curr;
            curr = next;
        }
        return prev;
    }
}