As you have seen the solutions may have a value occurring only once. Enjoy it!

You have two 1 in the first one and two -1 in the other.

The description fails to mention that the arrays in the solution should only contain unique values.

with this line:

int *result = malloc(length_in);

you do not allocate enough memory for an array of int of length length_in. the size of an array is not equal to its length, unless the array elements happen to have a size of one byte, which is not the case for int.

Please use the question tag to ask for help next time

Your allocated buffer is too small.

Please see: https://docs.codewars.com/references/markdown#code-block and post the code again, formatted in a readable way.

Would you be so kind to at least post your code, so we could check what is the problem with it? please remember about code blocks and spoiler flag!

Dennis, if you got the time and your solution at hand, please try it again. I think the problem is fixed...

I'll look at this in depth when at home, I'm very limited on the smartphone.
possibly test suite is broken , then...
would you mind posting your attempt?

edit: think I found the .mistake the namespace problem indeed is in the test suite. unable to solve it immediately ...

You are not supposed to "subtract" any rectangle from another. You are merely supposed to figure out the total area covered by at all.