4 KiB
4 KiB
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.
I commandeered a whiteboard for this.
