A fun but difficult unit on combinatorics problems involving rectangular grids.
Unit Overview
Grids, as the name suggests, is about grid-related combo problems. Its difficulty is probably around a mid-level Z unit, and it is very diverse in its problem set. The unit covers grid strategies from grid coloring to global-esque tactics to constructions, requiring a lot of material from other combo units like Global, Local, Equality, Free, Rigid, Induct, etc. It's almost like a "combo summit" but specifically aimed at problems with grids or problems that can be represented as a grid.
The walkthroughs cover a few grid strategies, leaving a lot of it for you to uncover on your own. Therefore, it is recommended to be well-grounded in combinatorics techniques before taking this.
Notable Problems
Some notable problems in this unit include:
- ISL 2009 C4 - Representative of the easier end of the problem set
- ISL 2014 C4 - Representative of the middle range of the problem set
- Serbia RMM TST 2017 - Representative of the harder range of the problem set
- China TST 2018/1/6 - A grid problem without a grid. Hard to say more without spoiling the problem ;-)