day 18 solution

2023/src/day18.rs

@@ -0,0 +1,123 @@
+use aoc_parse::{parser, prelude::*};
+use aoc_runner_derive::{aoc, aoc_generator};
+use std::ops::{Add, Div};
+
+#[derive(Clone, Copy)]
+enum Dir {
+    N,
+    E,
+    S,
+    W,
+}
+
+struct Move {
+    dir: Dir,
+    count: usize,
+    color: String,
+}
+
+#[aoc_generator(day18)]
+fn parse(input: &str) -> Vec<Move> {
+    let p = parser!(lines({ "U" => Dir::N, "R" => Dir::E, "D" => Dir::S, "L" => Dir::W } " " usize " (#" string(digit_hex+) ")"));
+    p.parse(input)
+        .unwrap()
+        .iter()
+        .map(|e| Move {
+            dir: e.0,
+            count: e.1,
+            color: e.2.clone(),
+        })
+        .collect::<Vec<_>>()
+}
+
+fn get_perimeter(moves: &[Move]) -> Vec<(isize, isize)> {
+    let mut c: (isize, isize) = (0, 0);
+    let mut r: Vec<(isize, isize)> = vec![];
+    r.push(c);
+    for m in moves.iter() {
+        match m.dir {
+            Dir::N => c.0 -= m.count as isize,
+            Dir::E => c.1 += m.count as isize,
+            Dir::S => c.0 += m.count as isize,
+            Dir::W => c.1 -= m.count as isize,
+        };
+        r.push(c);
+    }
+    r
+}
+
+fn distance(s: &(isize, isize), d: &(isize, isize)) -> usize {
+    s.0.abs_diff(d.0) + s.1.abs_diff(d.1)
+}
+
+fn shoelace(coords: &[(isize, isize)]) -> isize {
+    let len = coords.len();
+    let (area, perimeter) =
+        coords
+            .iter()
+            .enumerate()
+            .fold((0isize, 0isize), |(sum, perimeter), (index, c)| {
+                let c2 = coords[(index + 1) % len];
+                let next_perimeter = perimeter + distance(c, &c2) as isize;
+                let next_area = sum + (c.1 * c2.0) - (c.0 * c2.1);
+                (next_area, next_perimeter)
+            });
+
+    area.abs().add(perimeter).div(2).add(1)
+}
+
+#[aoc(day18, part1)]
+fn part1(input: &[Move]) -> isize {
+    shoelace(&get_perimeter(input))
+}
+
+#[aoc(day18, part2)]
+fn part2(input: &[Move]) -> isize {
+    let moves = input
+        .iter()
+        .map(|m| {
+            let mut s = m.color.clone();
+            let dir = match s.remove(s.len() - 1) {
+                '0' => Dir::E,
+                '1' => Dir::S,
+                '2' => Dir::W,
+                '3' => Dir::N,
+                n @ _ => panic!("parsed wrong number {}", n),
+            };
+            let count = usize::from_str_radix(&s, 16).unwrap();
+            Move {
+                dir,
+                count,
+                color: s,
+            }
+        })
+        .collect::<Vec<_>>();
+    shoelace(&get_perimeter(&moves))
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const SAMPLE_DATA: &'static str = r#"R 6 (#70c710)
+D 5 (#0dc571)
+L 2 (#5713f0)
+D 2 (#d2c081)
+R 2 (#59c680)
+D 2 (#411b91)
+L 5 (#8ceee2)
+U 2 (#caa173)
+L 1 (#1b58a2)
+U 2 (#caa171)
+R 2 (#7807d2)
+U 3 (#a77fa3)
+L 2 (#015232)
+U 2 (#7a21e3)"#;
+
+    #[test]
+    fn sample_data() {
+        let input = parse(&SAMPLE_DATA);
+        assert_eq!(part1(&input), 62);
+        assert_eq!(part2(&input), 952408144115);
+    }
+}

2023/src/lib.rs

@@ -17,5 +17,6 @@ mod day14;
 mod day15;
 mod day16;
 mod day17;
+mod day18;
 
 aoc_lib! { year = 2023 }