I had a similar problem, which I managed to find a way around. I'll add some hints below that may help.

Personally, I found this to be a harder than 7 kyu problem. I suspect it's because of the many ways Clojure can skin this cat, at least some of which have sub-optimal runtimes from an algorithmic perspective. Intuitively I would not expect a 7th kyu student to solve it. My idea is that such a student is still new to the lanuage, and may not find any but the most conspicuous runtime bugs. Put another way, if I were newly conversant in French, I could be expected, with some effort, to give accurate directions from the Louvre to Montmartre, but not good directions.

This works for me:

• From the solution editor, hit tab to enter the test editor.
• Enter: :w in normal mode
• Shift+tab to return to the solution editor.