June 7, 2018 The Writer’s Take on TCO18 Marathon Round 2

As I write this post, TCO Round 2 is still about 20 hours away. Problem testing is complete, the last of the four sample solutions (C#) is written, and I can spare some time to talk about the problem. In this I have an unfair advantage over the other bloggers, since I see not just the public face of the match but also the behind-the-scenes part of it.
By the time this post will see the light of day you’ll probably have read enough of the problem to know what it is about. You are given a set of crystals on a board, and you have to illuminate them with lights of certain colors, using colored light-emitters (called “lanterns”, though they are depicted as small suns and only emit light in four cardinal directions), mirrors to redirect the light rays and obstacles to stop light propagation.

This is clearly a game-inspired problem, as a lot of Marathons are. It combines two ideas – mixing primary colors to obtain required secondary colors and directing rays of light to specific destinations using mirrors. Both ideas are heavily exploited in various puzzles and games.
My absolute favorite among color-mixing games is Alchemistry, which combines this mechanics with planning and spatial thinking to fill the bottles with potions of the right colors in the right order. In fact, I was toying with the idea of converting this puzzle into a Marathon for quite some time, and dropped it only because I’m too lazy to code intersecting pipes on a hexagonal grid 🙂
The latest game with light and mirrors I’ve played is Quantum Game with Photons, which features wave optics and quantum mechanics, but also plain mirrors and the cutest light-absorbing rocks I’ve ever seen.
And the final push to write this problem was a game called Algemy. The previous games I’ve played were obviously rather complicated to implement and thus not terribly inspiring, but this one was just the right level to trigger the writer’s "aha" feeling.
Good luck in the match!
P.S. The unusual level of visualizer sophistication is entirely due to wleite’s efforts; the fanciest thing done by me is the nearly-diamond-cut of the crystals 🙂