public static SinglyLinkedListNode reverse(SinglyLinkedListNode llist) {
        if(llist == null) return null;
        if(llist.next == null) return llist;
        
        SinglyLinkedListNode curr = llist;
        SinglyLinkedListNode prev = null;
        SinglyLinkedListNode temp = null; 
        
        while(curr != null){
            temp = curr.next;
            //point curr node to prev
            curr.next = prev;
            //set prev = curr node
            prev = curr;
            curr = temp;
        }
        
        return prev;
    }