Day 17 solutions

aoc-solver/src/y2023/day17.rs

@@ -0,0 +1,258 @@
+use std::{
+    cmp::Ordering,
+    collections::{BinaryHeap, HashMap},
+};
+
+use itertools::Itertools;
+
+use crate::solution::{AocError, Solution};
+
+pub struct Day17;
+
+type Coords = (isize, isize);
+type Grid = Vec<Vec<u8>>;
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+enum Direction {
+    North,
+    East,
+    South,
+    West,
+}
+
+#[derive(Clone, Eq, PartialEq)]
+struct Search {
+    heat_loss: u32,
+    position: Coords,
+    direction: Direction,
+    consequtive: u8,
+}
+
+impl Ord for Search {
+    fn cmp(&self, other: &Self) -> Ordering {
+        other.heat_loss.cmp(&self.heat_loss)
+    }
+}
+
+impl PartialOrd for Search {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+fn parse(input: &str) -> Result<Grid, AocError> {
+    let grid: Grid = input
+        .trim()
+        .lines()
+        .map(|line| {
+            line.chars()
+                .map(|tile| {
+                    let heat_loss = tile
+                        .to_digit(10)
+                        .ok_or(AocError::parse(tile, "Invalid tile"))?;
+
+                    Ok(heat_loss as u8)
+                })
+                .try_collect()
+        })
+        .try_collect()?;
+
+    Ok(grid)
+}
+
+fn directions(
+    direction: &Direction,
+    consequtive: u8,
+    min_consequtive: u8,
+) -> Vec<(Direction, isize, isize)> {
+    if consequtive < min_consequtive {
+        return match direction {
+            Direction::North => vec![(Direction::North, 0, -1)],
+            Direction::East => vec![(Direction::East, 1, 0)],
+            Direction::South => vec![(Direction::South, 0, 1)],
+            Direction::West => vec![(Direction::West, -1, 0)],
+        };
+    }
+
+    match direction {
+        Direction::North => vec![
+            (Direction::North, 0, -1),
+            (Direction::East, 1, 0),
+            (Direction::West, -1, 0),
+        ],
+        Direction::East => vec![
+            (Direction::East, 1, 0),
+            (Direction::North, 0, -1),
+            (Direction::South, 0, 1),
+        ],
+        Direction::South => vec![
+            (Direction::South, 0, 1),
+            (Direction::East, 1, 0),
+            (Direction::West, -1, 0),
+        ],
+        Direction::West => vec![
+            (Direction::West, -1, 0),
+            (Direction::North, 0, -1),
+            (Direction::South, 0, 1),
+        ],
+    }
+}
+
+fn dijkstra(grid: &Grid, min_consequtive: u8, max_consequtive: u8) -> Option<u32> {
+    let mut heat_losses: HashMap<(Coords, Direction, u8), u32> = HashMap::new();
+    let mut heap: BinaryHeap<Search> = BinaryHeap::new();
+
+    let height = grid.len();
+    let width = grid[0].len();
+    let target = ((width - 1) as isize, (height - 1) as isize);
+
+    heap.push(Search {
+        position: (0, 0),
+        direction: Direction::East,
+        consequtive: 0,
+        heat_loss: 0,
+    });
+
+    while let Some(Search {
+        position,
+        direction,
+        consequtive,
+        heat_loss,
+    }) = heap.pop()
+    {
+        if position == target && consequtive >= min_consequtive {
+            return Some(heat_losses[&(position, direction, consequtive)]);
+        }
+
+        if heat_loss
+            > *heat_losses
+                .get(&(position, direction, consequtive))
+                .unwrap_or(&u32::MAX)
+        {
+            continue;
+        }
+
+        for (next_direction, dx, dy) in directions(&direction, consequtive, min_consequtive) {
+            let x = position.0 + dx;
+            let y = position.1 + dy;
+
+            if x >= 0 && y >= 0 && (x as usize) < width && (y as usize) < height {
+                let neighbour = grid[y as usize][x as usize];
+
+                let next_consequtive = if direction == next_direction {
+                    consequtive + 1
+                } else {
+                    1
+                };
+
+                if next_consequtive > max_consequtive {
+                    continue;
+                }
+
+                let next = Search {
+                    position: (x, y),
+                    direction: next_direction,
+                    heat_loss: heat_loss + neighbour as u32,
+                    consequtive: next_consequtive,
+                };
+
+                let best_known = heat_losses
+                    .entry((next.position, next.direction, next.consequtive))
+                    .or_insert(u32::MAX);
+
+                if next.heat_loss < *best_known {
+                    *best_known = next.heat_loss;
+                    heap.push(next)
+                }
+            }
+        }
+    }
+
+    None
+}
+
+impl Solution for Day17 {
+    type A = u32;
+    type B = u32;
+
+    fn default_input(&self) -> &'static str {
+        include_str!("../../../inputs/2023/day17.txt")
+    }
+
+    fn part_1(&self, input: &str) -> Result<u32, AocError> {
+        let grid = parse(input)?;
+        let total_heat_loss = dijkstra(&grid, 0, 3).ok_or(AocError::logic("No path found"))?;
+
+        Ok(total_heat_loss)
+    }
+
+    fn part_2(&self, input: &str) -> Result<u32, AocError> {
+        let grid = parse(input)?;
+        let total_heat_loss = dijkstra(&grid, 4, 10).ok_or(AocError::logic("No path found"))?;
+
+        Ok(total_heat_loss)
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn it_solves_part1_example() {
+        assert_eq!(
+            Day17.part_1(
+                "2413432311323\n\
+                 3215453535623\n\
+                 3255245654254\n\
+                 3446585845452\n\
+                 4546657867536\n\
+                 1438598798454\n\
+                 4457876987766\n\
+                 3637877979653\n\
+                 4654967986887\n\
+                 4564679986453\n\
+                 1224686865563\n\
+                 2546548887735\n\
+                 4322674655533\n"
+            ),
+            Ok(102)
+        );
+    }
+
+    #[test]
+    fn it_solves_part2_example_1() {
+        assert_eq!(
+            Day17.part_2(
+                "2413432311323\n\
+                 3215453535623\n\
+                 3255245654254\n\
+                 3446585845452\n\
+                 4546657867536\n\
+                 1438598798454\n\
+                 4457876987766\n\
+                 3637877979653\n\
+                 4654967986887\n\
+                 4564679986453\n\
+                 1224686865563\n\
+                 2546548887735\n\
+                 4322674655533\n"
+            ),
+            Ok(94)
+        );
+    }
+
+    #[test]
+    fn it_solves_part2_example_2() {
+        assert_eq!(
+            Day17.part_2(
+                "111111111111\n\
+                 999999999991\n\
+                 999999999991\n\
+                 999999999991\n\
+                 999999999991\n"
+            ),
+            Ok(71)
+        );
+    }
+}

aoc-solver/src/y2023/mod.rs

@@ -16,8 +16,9 @@ pub mod day13;
 pub mod day14;
 pub mod day15;
 pub mod day16;
+pub mod day17;
 
-pub const MAX_DAYS: u8 = 16;
+pub const MAX_DAYS: u8 = 17;
 
 pub struct Y2023;
 
@@ -40,6 +41,7 @@ impl Solver for Y2023 {
             14 => day14::Day14.run(input, 14, 2023),
             15 => day15::Day15.run(input, 15, 2023),
             16 => day16::Day16.run(input, 16, 2023),
+            17 => day17::Day17.run(input, 17, 2023),
             _ => vec![String::from("Solution not implemented (yet?)")],
         }
     }