static SinglyLinkedListNode mergeLists(SinglyLinkedListNode head1, SinglyLinkedListNode head2) {

        SinglyLinkedListNode newHead, temp;
        if(head1 == null)
            return head2;
        if (head2 == null)
            return head1;

        if(head1.data<head2.data) {
            newHead = temp = head1;
            head1 = head1.next;
            if(head1 == null) {
                newHead.next = head2;
            }
        }else {
            newHead = temp = head2;
            head2 = head2.next;
            if(head2 == null)
                newHead.next = head1;
        }
        while (head1 != null && head2 != null) {
            if(head1.data<head2.data) {
                temp.next = head1;
                temp = head1;
                head1 = head1.next;
                if(head1 == null) {
                    temp.next = head2;
                }
            } else {
                temp.next = head2;
                temp = head2;
                head2 = head2.next;
                if(head2 == null) {
                    temp.next = head1;
                }
            }
        }
        return newHead;

//        if(head1 == null) {
//            return head2;
//        }
//
//        if(head2 == null) {
//            return head1;
//        }
//
//        if(head1.data>head2.data){
//            SinglyLinkedListNode temp = head1;
//            head1 = head2;
//            head2 = temp;
//        }
//
//        SinglyLinkedListNode tempHeadA = head1;
//        SinglyLinkedListNode tempHeadB = head2;
//        SinglyLinkedListNode prevNode = null;
//
//        while (tempHeadA != null && tempHeadB != null){
//            if(tempHeadA.data<tempHeadB.data){
//                prevNode = tempHeadA;
//                tempHeadA = tempHeadA.next;
//            }else {
//                SinglyLinkedListNode next = tempHeadB.next;
//                prevNode.next = tempHeadB;
//                prevNode = tempHeadB;
//                tempHeadB.next = tempHeadA;
//                tempHeadB = next;
//            }
//        }
//
//        if(tempHeadA == null) {
//            prevNode.next = tempHeadB;
//        }
//        return head1;
    }