public static ListNode addInList(ListNode head1, ListNode head2) { // write code here Stack stack1 = new Stack<>(); while (head1 != null) { stack1.push(head1.val); head1 = head1.next; } Stack stack2 = new Stack<>(); while (head2 != null) { stack2.push(head2.val); head2 = head2.next; } ...