2024 day 10

Author: ictrobot

crates/year2024/examples/day10_example0.txt

@@ -0,0 +1,8 @@
+89010123
+78121874
+87430965
+96549874
+45678903
+32019012
+01329801
+10456732

crates/year2024/src/day10.rs

@@ -0,0 +1,120 @@
+use utils::grid;
+use utils::prelude::*;
+
+/// Counting increasing paths through a grid.
+#[derive(Clone, Debug)]
+pub struct Day10 {
+    rows: usize,
+    cols: usize,
+    grid: Vec<u32>,
+}
+
+impl Day10 {
+    pub fn new(input: &str, _: InputType) -> Result<Self, InputError> {
+        let (rows, cols, grid) = grid::from_str(input, |b| match b {
+            b'0'..=b'9' => Some((b - b'0') as u32),
+            _ => None,
+        })?;
+
+        Ok(Self { rows, cols, grid })
+    }
+
+    #[must_use]
+    pub fn part1(&self) -> u32 {
+        let mut total = 0;
+        let mut visited = vec![usize::MAX; self.grid.len()];
+        for r in 0..self.rows {
+            for c in 0..self.cols {
+                if self.grid[r * self.cols + c] != 0 {
+                    continue;
+                }
+                total += self.trailhead_score(r, c, 1, &mut visited, r * self.cols + c);
+            }
+        }
+        total
+    }
+
+    fn trailhead_score(
+        &self,
+        r: usize,
+        c: usize,
+        next: u32,
+        visited: &mut [usize],
+        visited_key: usize,
+    ) -> u32 {
+        let index = r * self.cols + c;
+        visited[index] = visited_key;
+        if next == 10 {
+            return 1;
+        }
+
+        let mut total = 0;
+        if r > 0
+            && self.grid[index - self.cols] == next
+            && visited[index - self.cols] != visited_key
+        {
+            total += self.trailhead_score(r - 1, c, next + 1, visited, visited_key);
+        }
+        if r < self.rows - 1
+            && self.grid[index + self.cols] == next
+            && visited[index + self.cols] != visited_key
+        {
+            total += self.trailhead_score(r + 1, c, next + 1, visited, visited_key);
+        }
+        if c > 0 && self.grid[index - 1] == next && visited[index - 1] != visited_key {
+            total += self.trailhead_score(r, c - 1, next + 1, visited, visited_key);
+        }
+        if c < self.cols - 1 && self.grid[index + 1] == next && visited[index + 1] != visited_key {
+            total += self.trailhead_score(r, c + 1, next + 1, visited, visited_key);
+        }
+
+        total
+    }
+
+    pub fn part2(&self) -> u32 {
+        let mut total = 0;
+        let mut cache = vec![None; self.grid.len()];
+        for r in 0..self.rows {
+            for c in 0..self.cols {
+                if self.grid[r * self.cols + c] != 0 {
+                    continue;
+                }
+                total += self.count_trails(r, c, 1, &mut cache);
+            }
+        }
+        total
+    }
+
+    fn count_trails(&self, r: usize, c: usize, next: u32, cache: &mut [Option<u32>]) -> u32 {
+        let index = r * self.cols + c;
+        if let Some(cache) = cache[index] {
+            return cache;
+        }
+
+        if next == 10 {
+            cache[index] = Some(1);
+            return 1;
+        }
+
+        let mut total = 0;
+        if r > 0 && self.grid[index - self.cols] == next {
+            total += self.count_trails(r - 1, c, next + 1, cache);
+        }
+        if r < self.rows - 1 && self.grid[index + self.cols] == next {
+            total += self.count_trails(r + 1, c, next + 1, cache);
+        }
+        if c > 0 && self.grid[index - 1] == next {
+            total += self.count_trails(r, c - 1, next + 1, cache);
+        }
+        if c < self.cols - 1 && self.grid[index + 1] == next {
+            total += self.count_trails(r, c + 1, next + 1, cache);
+        }
+
+        cache[index] = Some(total);
+        total
+    }
+}
+
+examples!(Day10 -> (u32, u32) [
+    {file: "day10_example0.txt", part1: 36, part2: 81},
+]);

crates/year2024/src/lib.rs

@@ -10,4 +10,5 @@ utils::year!(2024 => year2024, ${
     6 => day06::Day06,
     7 => day07::Day07,
     8 => day08::Day08,
+    10 => day10::Day10,
 });