Merge pull request #95 from jwodder/2024-12a

Solved 2024-12a

Author: jwodder

2024/12a/Cargo.toml

@@ -0,0 +1,16 @@
+[package]
+name = "advent-of-code-2024-12a"
+version = "0.1.0"
+edition.workspace = true
+rust-version.workspace = true
+description = "Solution to Advent of Code 2024, problem 12a"
+authors.workspace = true
+repository.workspace = true
+license.workspace = true
+publish.workspace = true
+
+[dependencies]
+adventutil = { path = "../../adventutil" }
+
+[lints]
+workspace = true

2024/12a/src/main.rs

@@ -0,0 +1,71 @@
+use adventutil::grid::{Direction, Grid};
+use adventutil::{components, Input};
+
+fn solve(input: Input) -> usize {
+    // Make this a reference to simplify the `move`-ing of `grid` into
+    // closures:
+    let grid = &input.parse::<Grid<char>>();
+    let comps = components(grid.iter_coords(), |c| {
+        Direction::cardinals().filter_map(move |d| {
+            grid.bounds()
+                .move_in(c, d)
+                .filter(|&c2| grid[c] == grid[c2])
+        })
+    });
+    let mut price = 0;
+    for region in &comps {
+        let area = region.len();
+        let perimeter: usize = region
+            .iter()
+            .map(|&c| {
+                Direction::cardinals()
+                    .filter(move |&d| {
+                        grid.bounds()
+                            .move_in(c, d)
+                            .is_none_or(|c2| !region.contains(&c2))
+                    })
+                    .count()
+            })
+            .sum();
+        price += area * perimeter;
+    }
+    price
+}
+
+fn main() {
+    println!("{}", solve(Input::from_env()));
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_example1() {
+        let input = Input::from("AAAA\nBBCD\nBBCC\nEEEC\n");
+        assert_eq!(solve(input), 140);
+    }
+
+    #[test]
+    fn test_example2() {
+        let input = Input::from("OOOOO\nOXOXO\nOOOOO\nOXOXO\nOOOOO\n");
+        assert_eq!(solve(input), 772);
+    }
+
+    #[test]
+    fn test_example3() {
+        let input = Input::from(concat!(
+            "RRRRIICCFF\n",
+            "RRRRIICCCF\n",
+            "VVRRRCCFFF\n",
+            "VVRCCCJFFF\n",
+            "VVVVCJJCFE\n",
+            "VVIVCCJJEE\n",
+            "VVIIICJJEE\n",
+            "MIIIIIJJEE\n",
+            "MIIISIJEEE\n",
+            "MMMISSJEEE\n",
+        ));
+        assert_eq!(solve(input), 1930);
+    }
+}