solution: day18

src/bin/18.rs

@@ -0,0 +1,89 @@
+use std::mem::swap;
+
+use itertools::Itertools;
+
+const DIRECTIONS: [(i32, i32); 8] = [
+    (1, 0),
+    (1, 1),
+    (0, 1),
+    (-1, 1),
+    (-1, 0),
+    (-1, -1),
+    (0, -1),
+    (1, -1),
+];
+
+fn count_surroundings(i: usize, j: usize, grid: &Vec<Vec<u32>>) -> u32 {
+    let mut count = 0;
+    for (di, dj) in DIRECTIONS.iter() {
+        let (ii, jj) = (i as i32 + di, j as i32 + dj);
+        if ii < 0 || jj < 0 || ii >= grid.len() as i32 || jj >= grid[0].len() as i32 {
+            continue;
+        }
+        count += grid[ii as usize][jj as usize];
+    }
+    count
+}
+
+fn conways_lights(input: &str, force_on: &[(usize, usize)]) -> Option<u32> {
+    let mut lights: Vec<Vec<u32>> = input
+        .lines()
+        .map(|x| {
+            x.chars()
+                .map(|y| match y {
+                    '.' => 0,
+                    '#' => 1,
+                    _ => unreachable!(),
+                })
+                .collect_vec()
+        })
+        .collect_vec();
+
+    let mut new_lights = lights.to_vec();
+
+    for _ in 0..100 {
+        for (i, j) in force_on.iter() {
+            lights[*i][*j] = 1;
+        }
+        for i in 0..lights.len() {
+            for j in 0..lights[i].len() {
+                match (lights[i][j], count_surroundings(i, j, &lights)) {
+                    (1, 2) | (_, 3) => new_lights[i][j] = 1,
+                    (_, _) => new_lights[i][j] = 0,
+                };
+            }
+        }
+        swap(&mut lights, &mut new_lights);
+    }
+    for (i, j) in force_on.iter() {
+        lights[*i][*j] = 1;
+    }
+    Some(lights.iter().map(|x| x.iter().sum::<u32>()).sum())
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    conways_lights(input, &[])
+}
+pub fn part_two(input: &str) -> Option<u32> {
+    let max = input.lines().collect_vec().len() - 1;
+    conways_lights(input, &[(0, 0), (0, max), (max, 0), (max, max)])
+}
+fn main() {
+    let input = &aoc::read_file("inputs", 18);
+    aoc::solve!(1, part_one, input);
+    aoc::solve!(2, part_two, input);
+}
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        let input = aoc::read_file("test_inputs", 18);
+        assert_eq!(part_one(&input), Some(4));
+    }
+    #[test]
+    fn test_part_two() {
+        let input = aoc::read_file("test_inputs", 18);
+        assert_eq!(part_two(&input), Some(7));
+    }
+}

src/test_inputs/18.txt

@@ -0,0 +1,6 @@
+.#.#.#
+...##.
+#....#
+..#...
+#.#..#
+####..