# Puzzle 20 – 20 parts

#1

The solution:

And the permalink:

https://www.lodev.org/jstumble/?board=rlerlf1fellfr1felrfrelflrfrelfrreei

In the one case where we need to send the blue ball right to hit the red lever, we know that the bits are afterwards in a position that leads to the interceptor. Hence, we can use the OR gate to replace the crossover and a whole bunch of ramps to get there.

I was trying to build a similar solution for Puzzle 19, but I’m not sure whether it’s fine if one or two additional red ball ends up in the tray at the bottom for some inputs?

Puzzle 19 – 20 parts
#2

Whoa - yep that’s a clear winner so far. Way less parts - nice work! It’s tricky how you send that red ball back through the switches to save parts.

#3

You can take advantage of the two crossover pieces to replace 4 ramps. Otherwise, not much to improve here. You need two full paths from the top bit to the interceptor/red release (the former not including the second bit; the latter passing through the second bit). You also need a path from the blue source to the top bit, and a path from the red source to the interceptor, which can’t merge with any existing paths any earlier than the top bit, so there’s 20 components worth of path - crossovers let you cheat that a bit by letting two paths pass through a single component.

https://www.lodev.org/jstumble/?board=rlerlf0fellfr0ferlfexferlfexferreei

#4

Ohhh, yeah. I discovered this technique more recently and didn’t think to revisit some earlier puzzles. Feel free to post that in a separate thread.

#5

I’m just going through the challenges for the 1st time. This was the same solution I came up with and I was questioning myself because I hadn’t used the crossovers. Gives valid results!