adventOfCode/challenges/2021/06-lanternfish

Day 6: Lanternfish

First, parse the input data into a usable form. Count the number of fish with each possible timer value (a given fish timer t must satisfy 0 <= t <= 8). Then, iterating can begin.

A single iteration does the following (in this case, the example input 3,4,3,1,2 is being used):

	-1	0	1	2	3	4	5	6	7	8
Initial starting timer frequencies		0	1	1	2	1	0	0	0	0
Shift input left	0	1	1	2	1	0	0	0	0
Add the value of -1 to the value of 6, and set the value of 8 to be equal to the value of -1, then remove the value for -1		1	1	2	1	0	0	0	0	0
Repeat		1	1	2	1	0	0	0	0	0
Shift input left	1	1	2	1	0	0	0	0	0
Add values		1	2	1	0	0	0	1	0	1
Repeat		1	2	1	0	0	0	1	0	1
Shift input left	1	2	1	0	0	0	1	0	1
Add values		2	1	0	0	0	1	1	1	1
Repeat		2	1	0	0	0	1	1	1	1
Shift input left	2	1	0	0	0	1	1	1	1
Add values		1	0	0	0	0	0	3	1	2
etc, etc.

Eventually, after the desired number of iterations, you can sum all the frequency values to get the challenge answer.

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I commandeered a whiteboard for this.