What custom data structure would you add?

Fun to revisit something I've done before, but the ambiguity of the -1 condition description soured it for me.

In case this helps:
You are being asked to comment on the snapshot of the game you are given. It could be finished, it could be unfinished. Your return is just commenting on the current state available.

Ahhhh, everyone used a much simpler method than I did. Doh! Oh well, I got to look up new stuffs.
It did take looking through the comments to figure out what I had to do (just adding the numbers in the array passes the test, so was thrown for a loop when tried to submit), but I'm glad I came back to this.
Thank you.

This was a really good kata for me, I got to learn new things about c# and dictionaries. Thank you for this :-)