Peter Vogel posted the following image on X yesterday.
The receive side of the coin is a decision tree for decoding Morse code. The shape is what makes this one interesting.
Decision trees are typically not very compact. Each branch is usually on its own horizontal level, with diagonal lines going down from each node to its children. But by making the lines either horizontal or vertical, the tree fits nicely into a circle.
I thought for a second that the designer had made the choices of horizontal or vertical segments in order to make the tree compact, but that’s not so. The direction of the path through the tree changes when and only when the Morse code switches from dot to dash or dash to dot.
It would be fun to play around with this, using the same design idea for other binary trees.