Statement says that length of string S is N characters. But statement says nothing about length of string T. It only says that T may be got from S using cyclic shifts. But there may be a mistake getting T from S. It is not said what kind of mistake can happen - only replacement of characters (then length of T must always be equal to the length of S) or also addition or removal of characters.

Now in all tests lengths of S and T are equal. I think that it would be better either to change statement (and say that length of T is also N characters) or add tests for different length S and T. In the second case _many_ authors (I estimate 3/4) would lose their ac.

Еxample of test that my program would fail:
1
a
aa