From 55833d081cf6e185aae9d9e0998d1696794a74ed Mon Sep 17 00:00:00 2001
From: uku <hi@uku.moe>
Date: Tue, 10 Dec 2024 21:55:34 +0100
Subject: [PATCH] feat(day10): init

---
 src/solutions/day_10.rs | 140 ++++++++++++++++++++++++++++++++++++++++
 src/solutions/mod.rs    |   2 +
 2 files changed, 142 insertions(+)
 create mode 100644 src/solutions/day_10.rs

diff --git a/src/solutions/day_10.rs b/src/solutions/day_10.rs
new file mode 100644
index 0000000..7eb532b
--- /dev/null
+++ b/src/solutions/day_10.rs
@@ -0,0 +1,140 @@
+use std::collections::HashSet;
+
+use crate::common::{Answer, Solution};
+
+pub struct Day10;
+
+impl Solution for Day10 {
+    fn name(&self) -> &'static str {
+        "Hoof It"
+    }
+
+    fn part_a(&self, input: &str) -> Answer {
+        let grid = input
+            .lines()
+            .map(|l| {
+                l.chars()
+                    .map(|c| c.to_digit(10).unwrap())
+                    .collect::<Vec<_>>()
+            })
+            .collect::<Vec<_>>();
+
+        grid.iter()
+            .enumerate()
+            .flat_map(|(x, l)| {
+                l.iter()
+                    .enumerate()
+                    .filter(|(_, n)| **n == 0)
+                    .map(move |(y, _)| (x, y))
+            })
+            .map(|(start_x, start_y)| {
+                let mut robots = HashSet::new();
+                robots.insert(Robot(start_x, start_y));
+
+                while !robots.iter().all(|r| r.is_done(&grid)) {
+                    robots = robots
+                        .into_iter()
+                        .flat_map(|r| r.propagate(&grid))
+                        .collect();
+                }
+
+                robots.len()
+            })
+            .sum::<usize>()
+            .into()
+    }
+
+    fn part_b(&self, input: &str) -> Answer {
+        let grid = input
+            .lines()
+            .map(|l| {
+                l.chars()
+                    .map(|c| c.to_digit(10).unwrap())
+                    .collect::<Vec<_>>()
+            })
+            .collect::<Vec<_>>();
+
+        grid.iter()
+            .enumerate()
+            .flat_map(|(x, l)| {
+                l.iter()
+                    .enumerate()
+                    .filter(|(_, n)| **n == 0)
+                    .map(move |(y, _)| (x, y))
+            })
+            .map(|(start_x, start_y)| {
+                let mut robots = vec![Robot(start_x, start_y)];
+
+                while !robots.iter().all(|r| r.is_done(&grid)) {
+                    robots = robots
+                        .into_iter()
+                        .flat_map(|r| r.propagate(&grid))
+                        .collect();
+                }
+
+                robots.len()
+            })
+            .sum::<usize>()
+            .into()
+    }
+}
+
+#[derive(Debug, Hash, PartialEq, Eq)]
+struct Robot(usize, usize);
+
+impl Robot {
+    fn is_done(&self, grid: &[Vec<u32>]) -> bool {
+        grid[self.0][self.1] == 9
+    }
+
+    fn propagate(self, grid: &[Vec<u32>]) -> Vec<Self> {
+        if self.is_done(grid) {
+            vec![self]
+        } else {
+            let max_x = grid.len() - 1;
+            let max_y = grid[0].len() - 1;
+            let current = grid[self.0][self.1];
+
+            [
+                self.0.checked_sub(1).map(|n| (n, self.1)),
+                (self.0 < max_x).then(|| (self.0 + 1, self.1)),
+                self.1.checked_sub(1).map(|n| (self.0, n)),
+                (self.1 < max_y).then(|| (self.0, self.1 + 1)),
+            ]
+            .iter()
+            .filter_map(|o| *o)
+            .filter(|(x, y)| grid[*x][*y] == current + 1)
+            .map(|(x, y)| Self(x, y))
+            .collect()
+        }
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use super::Day10;
+    use crate::common::Solution;
+
+    use indoc::indoc;
+
+    const INPUT: &str = indoc! {"
+        89010123
+        78121874
+        87430965
+        96549874
+        45678903
+        32019012
+        01329801
+        10456732
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(Day10.part_a(INPUT), 36.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(Day10.part_b(INPUT), 81.into());
+    }
+}
diff --git a/src/solutions/mod.rs b/src/solutions/mod.rs
index c5c69cf..c4d30ca 100644
--- a/src/solutions/mod.rs
+++ b/src/solutions/mod.rs
@@ -9,6 +9,7 @@ mod day_06;
 mod day_07;
 mod day_08;
 mod day_09;
+mod day_10;
 
 pub const SOLUTIONS: &[&dyn Solution] = &[
     &day_01::Day01,
@@ -20,4 +21,5 @@ pub const SOLUTIONS: &[&dyn Solution] = &[
     &day_07::Day07,
     &day_08::Day08,
     &day_09::Day09,
+    &day_10::Day10,
 ];