your solution writes past the end of the output buffer: you are printing a trailing '.', and then erase it. this is not robust: the worst-case output size is 16 i.e. strlen("100.100.100.100") + 1, so the caller of the function can expect that 16 bytes should be enough, but your solution needs more bytes than that. as a result of writing out-of-bounds, you corrupt the tests suite

I'm using c and I get a weird error: Your solution has memory leak, expected max length 15 + 1 '\0' = 16..
I tried printing the length of the problematic result on my pc and it is 15, meaning 16 with the null character.
What is the problem?

Very good kata not wanting me to figure out how it works. Only thing is that input and output could have been int array. I didn't realize there were helper functions in the c kata, so I had to use fucking strtok.

Should it really be? I think this is on the easier side of 6 kyu. Btw, g964, very good kata.

They do.

Very nice kata. I think, the tests should contain numbers too, especially since they aren't treated like letters.

Adding strings is very slow. Either use strings.Builder, or allocate a rune array beforehand, since you already know the size.