This post in Code Jam group
I want to discuss interactive problems in Code Jam. Code Jam didn't have interactive problems until recently, and there are still major differences between interactive problems in Code Jam versus the other competitions where interactive problems are more established.
One difference is in how sample interactions are presented. I think that in Code Jam, sample interactions are very inconvenient to read. For regular input and output, there is a place where you can read just the input and just the output, but for interactive problems, you have to read a mix of pseudocode, comments and the actual input/output.
Other competitions that have interactive problems usually use more concise formats, which are easier to read quickly. One possibility is to just present the input and the output separately, like here (problems H and I). This doesn't convey the relative order of the input and output lines, but it can be reconstructed from the description of the interaction protocol. Also, it is possible to use empty lines to show the order, like here (problem C). There are multiple approaches that can be used to show a sample interaction in a single column, like showing input and output lines in different colors, or prefixing them with different symbols (for example, left and right arrows). In all cases, it is possible to add an additional column for comments.
Another feature of interactive problems specific to Code Jam is that when a solution produces an incorrect result, the judge program will communicate this to the solution and wait for it to terminate. This doesn't make sense. Once the solution produces an incorrect result, there is no point in continuing to run it, and in other competitions, it would be immediately terminated in such a situation. But apparently Code Jam team expects the contestants to write code that would check the judge's output and handle the case where it indicates that the solution's output is incorrect. This is useless, because it wouldn't make any solution pass that wouldn't pass otherwise, and that's all that matters for a solution. I for one don't write such code (my solutions always skip this part of the judge's output), but I still need to not forget to read (and ignore) that line, something that I don't have to do in other competitions.
Finally, I'd prefer sample interactions to be correct. It's simple: for regular problems, sample inputs and outputs are (almost) always correct, so why should it be any different for interactive problems? Yet, both of this year's interactive problems available so far have sample interactions where a solution provides an incorrect answer, apparently to demonstrate the judge's response to it (the right response, as I already said, is to terminate the solution with WA verdict).
What do you think of all this?