static SinglyLinkedListNode mergeLists(SinglyLinkedListNode head1, SinglyLinkedListNode head2) {
        //handle edge cases where there is no other list to merge
        if(head1 == null) return head2;
        if(head2 == null) return head1;
        
        //determine the new head of the merged linked list
        SinglyLinkedListNode head;
        if(head1.data <= head2.data){
            head = head1;
            head1 = head1.next;
        }
        else{
            head = head2;
            head2 = head2.next;
        }
        
        //iterate through both linked lists, sorting asc
        SinglyLinkedListNode curr = head;
        while(head1 != null && head2 != null){
            if(head1.data <= head2.data){
                curr.next = head1;
                head1 = head1.next;
            }
            else{
                curr.next = head2;
                head2 = head2.next;
            }
            curr = curr.next;
        }
        
        //append any extra vals to the merged linked list
        if(head1 != null) curr.next = head1;
        else if(head2 != null) curr.next = head2;
        
        return head;
    }