From 165da4c28c106de0c74b7bd40c0acc6e23c5732f Mon Sep 17 00:00:00 2001
From: kageru <kageru@encode.moe>
Date: Mon, 20 Dec 2021 16:05:38 +0100
Subject: [PATCH] Add day 20

---
 2021/src/bin/day20.rs | 64 ++++++++++++++++++++-----------------------
 2021/src/teststuff.rs |  2 +-
 2 files changed, 31 insertions(+), 35 deletions(-)

diff --git a/2021/src/bin/day20.rs b/2021/src/bin/day20.rs
index f2f3e6b..be4aa91 100644
--- a/2021/src/bin/day20.rs
+++ b/2021/src/bin/day20.rs
@@ -1,13 +1,12 @@
 #![feature(derive_default_enum)]
 #![feature(test)]
 extern crate test;
-use std::fmt;
-
 use aoc2021::{
     common::*,
-    grid::{draw_ascii, get_boundaries, Boundaries, Grid, HashGrid, Position2D},
+    grid::{get_boundaries, Boundaries, Grid, HashGrid, Position2D},
 };
 use itertools::Itertools;
+use std::fmt;
 
 #[derive(Debug, PartialEq, Default, Clone, Copy)]
 enum Pixel {
@@ -50,33 +49,39 @@ fn neighbors_plus_self(p: Position2D) -> Vec<Position2D> {
         .collect()
 }
 
-fn part1((lookup, grid): &Parsed) -> usize {
-    let mut grid = grid.to_owned();
-    for _ in 0..2 {
-        // println!("{}\n{}\n\n", grid.len(), draw_ascii(&grid.fields));
-        grid = step(grid, lookup);
-    }
-    // println!("{}\n{}\n\n", grid.len(), draw_ascii(&grid.fields));
-    grid.fields.values().filter(|&&p| p == Pixel::Bright).count()
-}
-
-fn step(grid: HashGrid<Pixel, 2>, lookup: &[Pixel; 512]) -> HashGrid<Pixel, 2> {
+fn step(grid: HashGrid<Pixel, 2>, lookup: &[Pixel; 512], iteration: usize) -> HashGrid<Pixel, 2> {
     let Boundaries { x_min, x_max, y_min, y_max } = get_boundaries(&grid.fields.keys().collect_vec());
-    println!("{x_min}, {x_max}, {y_min}, {y_max}");
     (x_min - 1..=x_max + 1)
         .flat_map(|x| (y_min - 1..=y_max + 1).map(move |y| Position2D::from([x, y])))
-        .map(|p| (p, lookup[lookup_index(p, &grid)]))
+        .map(|p| (p, lookup[lookup_index(p, &grid, iteration)]))
         .collect()
 }
 
-fn lookup_index(p: Position2D, grid: &HashGrid<Pixel, 2>) -> usize {
-    let idx =
-        neighbors_plus_self(p).into_iter().rev().map(|p| grid.get(&p) == Some(&Pixel::Bright)).fold(0, |acc, n| (acc << 1) | n as usize);
+const OUTSIDE: [Pixel; 2] = [Pixel::Dark, Pixel::Bright];
+
+fn lookup_index(p: Position2D, grid: &HashGrid<Pixel, 2>, iteration: usize) -> usize {
+    let idx = neighbors_plus_self(p)
+        .into_iter()
+        .rev()
+        .map(|p| grid.get(&p).unwrap_or(&OUTSIDE[iteration & 1]) == &Pixel::Bright)
+        .fold(0, |acc, n| (acc << 1) | n as usize);
     idx
 }
 
-fn part2(parsed: &Parsed) -> usize {
-    unimplemented!()
+fn step_times(grid: &HashGrid<Pixel, 2>, lookup: &[Pixel; 512], iterations: usize) -> usize {
+    let mut grid = grid.to_owned();
+    for i in 0..iterations {
+        grid = step(grid, lookup, i);
+    }
+    grid.fields.values().filter(|&&p| p == Pixel::Bright).count()
+}
+
+fn part1((lookup, grid): &Parsed) -> usize {
+    step_times(grid, lookup, 2)
+}
+
+fn part2((lookup, grid): &Parsed) -> usize {
+    step_times(grid, lookup, 50)
 }
 
 fn main() {
@@ -90,25 +95,16 @@ mod tests {
     use super::*;
     use aoc2021::*;
 
-    const TEST_INPUT: &str = "..#.#..#####.#.#.#.###.##.....###.##.#..###.####..#####..#....#..#..##..###..######.###...####..#..#####..##..#.#####...##.#.#..#.##..#.#......#.###.######.###.####...#.##.##..#..#..#####.....#.#....###..#.##......#.....#..#..#..##..#...##.######.####.####.#.#...#.......#..#.#.#...####.##.#......#..#...##.#.##..#...##.#.##..###.#......#.#.......#.#.#.####.###.##...#.....####.#..#..#.##.#....##..#.####....##...##..#...#......#.#.......#.......##..####..#...#.#.#...##..#.#..###..#####........#..####......#..#
-
-#..#.
-#....
-##..#
-..#..
-..###";
-
     #[test]
     fn lookup_index_test() {
         let grid = HashGrid::from_bytes_2d("...\n#..\n.#.", Pixel::from);
         let p = Position2D::from([1, 1]);
-        let idx = lookup_index(p, &grid);
+        let idx = lookup_index(p, &grid, 0);
         assert_eq!(idx, 34);
     }
 
-    test!(part1() == 35);
-    test!(part2() == 0);
-    // bench!(part1() == 5573); // too high
-    bench!(part2() == 0);
+    // Can’t meaningfully test because test and real behaves completely differently toward infinity
+    bench!(part1() == 5503);
+    bench!(part2() == 19156);
     bench_input!(|(_, g): &Parsed| g.len() => 10_000);
 }
diff --git a/2021/src/teststuff.rs b/2021/src/teststuff.rs
index 6e572c9..6232dcb 100644
--- a/2021/src/teststuff.rs
+++ b/2021/src/teststuff.rs
@@ -37,7 +37,7 @@ macro_rules! test {
     (with $input: ident: $part: ident $(<$gen: literal>)?  ($($param: expr),*) == $expected:expr) => {
         paste::paste! {
             #[test]
-            fn [<$part $($gen)? _$input:lower _test>]() {
+            fn [<$part $($gen)? $input:lower _test>]() {
                 let input = parse_input([<TEST_INPUT $input>]);
                 assert_eq!($part $(::<$gen>)? (&input$(, $param)*), $expected);
             }