After a group is fully expanded, nothing appears beyond the final closing parenthesis.

Such inputs are not possible. Each expression should be connected only to one pair of braces. In other words, you can't have abbcdd -> a(2(b))(c(2(d))), cause the structure of this input is a()() and you can't have () after the first ().

It would be brilliant if you knew all the task.

Also this code can not solve such task: a2(b)c2(d)
It gives the result: abcddbcdd
But the right result is: abbcdd

How can we make our program better? We do many tests and change it to get the correct result. Of course, we know all the input data and according to it change our code. How can I improve my code for solving this kata? I passed all the long tests (long sentences). It means, that my code is useful for any real situation. But I can not solve other small tests. I am disappointed...

Всегда было интересно. Каково в последствии править такой код? Вот нахера всё лепить в одну строку?