Stacking Code

Following on from the previous challenges, I finally got around to doing December's coding challenge. After two attempts and two silver awards, I got a golden award on my third attempt. My first attempt was a naive solution to get my head around the problem and set up test cases. The second solution was better, but still didn't handle consecutive plots with large height differences in a performant way. As usual the expected complexity gives a big clue on how to go about solving the problem with full marks.