I'm doing the Advent of Code 2020. This repo contains my solutions.
My goals for this project are to:
- Gain fluency in Golang.
- Learn to better write Unit Tests.
- Get the correct solutions.
My goals for this project are not:
- Be the first to complete any problems.
- Write 'the best' solution, whatever that means.
The basic approach works here:
- Sort the input.
- Count the Jumps of Ones and Threes.
- Don't forget the additional Three at the end (device adaptor) or to insert a zero at the start (power outlet). Because I did.
- Looking at the sorted input, I can see that there are no jumps of 2, only jumps of 1 or 3.
- Since a jump of 3 is the maximum allowable, the possible paths 'converge' at these points. Therefore I can split the sequence into smaller, monotonically increasing sequences. I can more easily calculate the total paths in these, and multiply them together.
- It turns out these follow a sequence, where the number of paths in a sequence is the sum of the previous three entries in the sequence: 1,1,2,4,7,13 ...
- Floating Point Math is expensive, therefore use integer rules.
- A rotation of 180° is simply a sign change such that
x,y -> -x,-y - A rotation of +270° = -90° and so on.
- For clockwise turns,
x,y(+90°) = y,-x(0°). - For widdershins turns,
x,y(-90°) = -y,x(0°). - This is all a lot easier if you assume the origin for the waypoint is the boat.