day4: part1

src/day4.rs

@@ -0,0 +1,47 @@
+use aoc_runner_derive::{aoc, aoc_generator};
+use grid::Grid;
+
+#[aoc_generator(day4)]
+fn parse(input: &str) -> Grid<u8> {
+    input.parse().unwrap()
+}
+
+#[aoc(day4, part1)]
+fn part1(input: &Grid<u8>) -> u64 {
+    (0..input.height() * input.width())
+        .filter(|i| *input.get(&input.coord(*i as i64).unwrap()).unwrap() == b'@')
+        .map(|i| input.neighbours_count(input.coord(i as i64).unwrap(), |c| *c == b'@'))
+        .filter(|n| *n < 4)
+        .count() as u64
+}
+
+#[aoc(day4, part2)]
+fn part2(input: &Grid<u8>) -> u64 {
+    input.width() as u64
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const EXAMPLE: &str = "..@@.@@@@.
+@@@.@.@.@@
+@@@@@.@.@@
+@.@@@@..@.
+@@.@@@@.@@
+.@@@@@@@.@
+.@.@.@.@@@
+@.@@@.@@@@
+.@@@@@@@@.
+@.@.@@@.@.";
+
+    #[test]
+    fn part1_example() {
+        assert_eq!(part1(&parse(EXAMPLE)), 13);
+    }
+
+    #[test]
+    fn part2_example() {
+        assert_eq!(part2(&parse(EXAMPLE)), 0);
+    }
+}

src/lib.rs

@@ -1,6 +1,7 @@
 mod day1;
 mod day2;
 mod day3;
+mod day4;
 
 use aoc_runner_derive::aoc_lib;