Add day 6 solutions. Both, naive and more elaborate.

The naive implementation uses simple ring buffers and scales linearly
with the number of days needed.
The matrix based implementation uses matrix multiplication (implemented
in a brain-dead way inline here) and has the same scaling behaviour,
however implementing it showed that the matrix is correct.
The closed form is, well, a closed form based on the matrix based
solution, but working in the matrix' Eigenspace.

1 files changed, 1 insertions, 0 deletions

diff --git a/src/lib.rs b/src/lib.rs
index 66130bd..a558ff4 100644
--- a/src/lib.rs
+++ b/src/lib.rs
@@ -5,5 +5,6 @@ pub mod day2;
 pub mod day3;
 pub mod day4;
 pub mod day5;
+pub mod day6;
 
 aoc_lib!{ year = 2021 }