IC: Invalid Character
Invalid Character
IC ()
Although your program did not crash with any test case, and it was fast enough compared to the Jutge's solution, at least one of its outputs for some test case includes some 'strange' character, which is neither a tab (that should never be printed anyway), nor a mark of end-of-line, nor any character with ASCII code in the range 32-126. Perhaps your program prints characters with accents or alike.

In the case of graphic problems, IC means that the output graphic was not generated or that its width or its height are incorrect. Check the creation of file output.png and check its size.