Here’s my solution (it’s the one from the book):

And here’s the link:

http://www.lodev.org/jstumble/?board=11llrrr0e0lellrrer0e0lellrrerre0lerrlleerilfrleex

**Description:** This solution adds numbers by counting down on the left register while right register counts up.

This is actually not the most efficient way to add numbers, but conceptually it is the easiest to understand. Puzzle 47 uses a more efficient method.