fair enough, sorry about that

I did not have mistake in the code, I have changed my code to use heap allocation, because my solution with static char array was not passing the tests because of the crash caused by hidden free.

OP solved the kata. please come back to close your issues / questions once you found the mistake in your code.

meanwhile, I just added a comment to the solution set-up that mentions allocation / freeing

I just ran the current version of your solution and it passed all tests.

?

Getting crash in C, free(invalid pointer), but I ma not freeing anything and the kata does not ask for heap allocated string.

Self approved after 4 years :-)

Forked and approved

Random tests of all languages do not generate empty strings

this is already handled there

Enabled in this fork

Enabled in this fork

In Python returning -1 is probably less good tnan None.