Complete day 15

Cargo.lock

@@ -123,3 +123,11 @@ dependencies = [
  "anyhow",
  "common",
 ]
+
+[[package]]
+name = "day15"
+version = "0.1.0"
+dependencies = [
+ "anyhow",
+ "common",
+]

crates/day15/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "day15"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+anyhow = "1.0"
+common = { path = "../common" }

crates/day15/src/input/input.txt

@@ -0,0 +1,100 @@
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crates/day15/src/input/test.txt

@@ -0,0 +1,10 @@
+1163751742
+1381373672
+2136511328
+3694931569
+7463417111
+1319128137
+1359912421
+3125421639
+1293138521
+2311944581

crates/day15/src/main.rs

@@ -0,0 +1,229 @@
+use anyhow::{anyhow, Result};
+use common::instrument;
+use std::cmp::{Ord, Ordering, PartialOrd};
+use std::collections::{BinaryHeap, HashMap};
+use std::convert::From;
+
+const INPUT: &str = include_str!("input/input.txt");
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+struct Point {
+    x: i32,
+    y: i32,
+}
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
+struct OpenPoint {
+    x: i32,
+    y: i32,
+    f_score: i32,
+}
+
+impl Ord for OpenPoint {
+    fn cmp(&self, other: &Self) -> Ordering {
+        other.f_score.cmp(&self.f_score)
+    }
+}
+
+impl PartialOrd for OpenPoint {
+    fn partial_cmp(&self, other: &Self) -> Option<Ordering> {
+        Some(self.cmp(other))
+    }
+}
+
+impl From<Point> for OpenPoint {
+    fn from(point: Point) -> Self {
+        OpenPoint {
+            x: point.x,
+            y: point.y,
+            f_score: 0,
+        }
+    }
+}
+
+impl From<OpenPoint> for Point {
+    fn from(open_point: OpenPoint) -> Self {
+        Point {
+            x: open_point.x,
+            y: open_point.y,
+        }
+    }
+}
+
+impl Point {
+    fn manhattan_distance(&self, other: &Point) -> usize {
+        ((self.x - other.x).abs() + (self.y - other.y).abs()) as usize
+    }
+}
+
+fn reconstruct_path(came_from: &HashMap<Point, Point>, current: Point, start: Point) -> Vec<Point> {
+    let mut path = vec![current];
+    let mut current = current;
+    loop {
+        current = came_from[&current];
+        if current == start {
+            break;
+        }
+        path.push(current);
+    }
+    path
+}
+
+fn find_shortest_path(grid: &Vec<Vec<usize>>) -> Result<Vec<Point>> {
+    let destination = Point {
+        x: grid[0].len() as i32 - 1,
+        y: grid.len() as i32 - 1,
+    };
+    let mut open_list = BinaryHeap::new();
+    open_list.push(OpenPoint {
+        x: 0,
+        y: 0,
+        f_score: 0,
+    });
+    let mut came_from = HashMap::new();
+    let mut g_score = HashMap::new();
+    g_score.insert(Point { x: 0, y: 0 }, 0);
+    let mut f_score = HashMap::new();
+    f_score.insert(Point { x: 0, y: 0 }, 0);
+
+    // A* algorithm
+    while !open_list.is_empty() {
+        let current = open_list.pop().unwrap();
+        if current.x == destination.x && current.y == destination.y {
+            let path = reconstruct_path(&came_from, current.into(), Point { x: 0, y: 0 });
+            return Ok(path);
+        }
+
+        let mut neighbors = vec![];
+        if current.x > 0 {
+            neighbors.push(Point {
+                x: current.x - 1,
+                y: current.y,
+            });
+        }
+        if current.x < grid.len() as i32 - 1 {
+            neighbors.push(Point {
+                x: current.x + 1,
+                y: current.y,
+            });
+        }
+        if current.y > 0 {
+            neighbors.push(Point {
+                x: current.x,
+                y: current.y - 1,
+            });
+        }
+        if current.y < grid[0].len() as i32 - 1 {
+            neighbors.push(Point {
+                x: current.x,
+                y: current.y + 1,
+            });
+        }
+
+        for neighbor in neighbors {
+            let tentative_g_score =
+                g_score[&current.into()] + grid[neighbor.y as usize][neighbor.x as usize];
+
+            let neighbor_g_score = *g_score.get(&neighbor).unwrap_or(&std::usize::MAX);
+            if tentative_g_score < neighbor_g_score {
+                came_from.insert(neighbor, current.into());
+                g_score.insert(neighbor, tentative_g_score);
+                let neighbor_f_score =
+                    tentative_g_score + neighbor.manhattan_distance(&destination);
+                f_score.insert(neighbor, neighbor_f_score);
+                if open_list
+                    .iter()
+                    .find(|&p| p.x == neighbor.x && p.y == neighbor.y)
+                    == None
+                {
+                    open_list.push(OpenPoint {
+                        x: neighbor.x,
+                        y: neighbor.y,
+                        f_score: neighbor_f_score as i32,
+                    });
+                }
+            }
+        }
+    }
+
+    Err(anyhow!("no path found"))
+}
+
+fn solve_part1(input: &str) -> Result<i32> {
+    let lines = input.trim().lines();
+    let mut grid = vec![];
+
+    for line in lines {
+        let mut row = vec![];
+        for c in line.chars() {
+            row.push(c.to_digit(10).ok_or(anyhow!("invalid risk level"))? as usize);
+        }
+        grid.push(row);
+    }
+
+    let path = find_shortest_path(&grid)?;
+    Ok(path
+        .iter()
+        .map(|p| grid[p.y as usize][p.x as usize] as i32)
+        .sum())
+}
+
+fn expand_grid(grid: &Vec<Vec<usize>>, n: usize) -> Vec<Vec<usize>> {
+    let mut new_grid = vec![];
+    for y in 0..(grid.len() * n) {
+        let mut new_row = vec![];
+        for x in 0..(grid[0].len() * n) {
+            let mut orig = grid[y % grid.len()][x % grid[0].len()];
+            orig += x / grid[0].len() + y / grid.len();
+            if orig > 9 {
+                orig = (orig % 10) + 1;
+            }
+            new_row.push(orig);
+        }
+        new_grid.push(new_row);
+    }
+
+    new_grid
+}
+
+fn solve_part2(input: &str) -> Result<i32> {
+    let lines = input.trim().lines();
+    let mut grid = vec![];
+
+    for line in lines {
+        let mut row = vec![];
+        for c in line.chars() {
+            row.push(c.to_digit(10).ok_or(anyhow!("invalid risk level"))? as usize);
+        }
+        grid.push(row);
+    }
+
+    let grid = expand_grid(&grid, 5);
+
+    let path = find_shortest_path(&grid)?;
+    Ok(path
+        .iter()
+        .map(|p| grid[p.y as usize][p.x as usize] as i32)
+        .sum())
+}
+
+fn main() {
+    instrument!(solve_part1(INPUT).unwrap(), solve_part2(INPUT).unwrap());
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    const TEST_INPUT: &str = include_str!("input/test.txt");
+
+    #[test]
+    fn solves_part1() {
+        assert_eq!(solve_part1(TEST_INPUT).unwrap(), 40);
+    }
+
+    #[test]
+    fn solves_part2() {
+        assert_eq!(solve_part2(TEST_INPUT).unwrap(), 315);
+    }
+}