Google Code Jam 2021 Round 2 Screencast + Commentary

Screencast and some discussion while solving Round 2 of this year's GCJ. See below for the outcome. As mentioned in the video, I plan to stream GCJ practice at https://twitch.tv/snapdragon64 on Friday evenings (9:00 PDT). It'll be mostly the same format, but I'll also answer questions. Timestamps: 00:00 Intro 01:52 A - Minimum Sort 14:37 B - Matrygons 36:38 C - Hidden Pancakes 1:15:18 D - Retiling 1:55:09 Summary (not in video) Fixing D :( Shortly after stopping the video, I realized my D was broken - using max edge cost for flow rather than sum of edge costs. It wasn't backtracking correctly, so I have no idea how this managed to pass the Visible test case! I had to quickly rewrite my min-cost-max-flow into a Bellman-Ford based solution, and I apologize that this isn't included in the video. In the end, I passed all problems, coming in 258th. This was a really fast round of easier-than-expected problems, which does not play to my strengths. I missed a trivial solution for B, missed a fairly obvious approach to C, and didn't have a precoded min-cost-max-flow for D. Ouch!