Nice short thinking exercise. I hadn't implemented this before, but was pretty straightforward. I setup an array with the code and a position marker. Catch all keyboard entries, when the user enters the correct key for the next step of the code, move the marker, otherwise reset the marker to the first item. If after moving the marker, we are at the end of the code, reveal the secret.

This is the first exercise where after watching the video, I felt like my solution was better than the one shown in the video.

Completion Time: ~5 Minutes

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You can view my key-sequence-detector here (code: up-down-up-down-left-right-left-right-b-a):

You can see my code here: