[asiekierka]

Doe it literally check for the specific solution?

Writing

    to = append(to, ctrl)

which is functionally equivalent and, in my personal opinion, with clearer intent (ctrl = 0 at that point in the code), returns "incorrect".

In fact, it seems that any placeholder value should work - as it is always overwritten by the final value of ctrl for a given set of bytes at the end; however, the checker rejects this.

[bugfix-66]

Your fix is wrong, so the site rejects it.

Go doesn't do integer type conversions implicitly, to avoid the implicit-type-casting bugs endemic to C. Go (thankfully) doesn't allow an implicit conversion from int to byte. You must do the cast explicitly.

So you would have to say

  to = append(to, byte(ctrl))

and that's correct.

The site builds and executes the code you submit, and any correct solution is accepted.