Add day08, 2022

1 files changed, 211 insertions, 0 deletions

diff --git a/2022/rust/day08/src/main.rs b/2022/rust/day08/src/main.rs
new file mode 100644
index 0000000..1a17d93
--- /dev/null
+++ b/2022/rust/day08/src/main.rs
@@ -0,0 +1,211 @@
+use {
+    anyhow::{
+        anyhow,
+        Context,
+        Result,
+    },
+    std::{
+        env::args,
+        fs::File,
+        io::{
+            BufRead,
+            BufReader,
+        },
+        path::Path,
+    },
+};
+
+#[derive(Clone,Copy,Debug)]
+enum Direction {
+    Up,
+    Down,
+    Left,
+    Right,
+}
+
+#[derive(Clone,Debug,PartialEq)]
+struct Position {
+    x: usize,
+    y: usize,
+}
+
+#[derive(Debug)]
+struct Trees {
+    size: usize,
+    heights: Vec<u8>,
+}
+
+impl Trees {
+    fn new_with_size(size: usize, heights: Vec<u8>) -> Result<Self> {
+        let len = heights.len();
+        if size * size == len {
+            Ok(Self { size, heights, })
+        } else {
+            Err(anyhow!("Could not create Trees: {size}² ≠ {len}."))
+        }
+    }
+
+    fn size(&self) -> usize {
+        self.size
+    }
+
+    fn height(&self, position: &Position) -> u8 {
+        let x = position.x as usize;
+        let y = position.y as usize;
+        if let Some(height) = self.heights.get(y * self.size + x) {
+            *height
+        } else {
+            panic!("Invalid attempt to access element x: {x}, y: {y} in Trees with size: {}.",
+                self.size);
+        }
+    }
+
+    fn is_visible(&self, position: &Position, direction: Direction) -> bool {
+        let target_height = self.height(position);
+
+        match direction {
+            Direction::Up => {
+                for distance in 0..position.y {
+                    let cmp_height = self.height(&Position { x: position.x, y: distance });
+                    if cmp_height >= target_height {
+                        return false;
+                    }
+                }
+            },
+            Direction::Down => {
+                for distance in (position.y + 1)..self.size {
+                    let cmp_height = self.height(&Position { x: position.x, y: distance });
+                    if cmp_height >= target_height {
+                        return false;
+                    }
+                }
+            },
+            Direction::Left => {
+                for distance in 0..position.x {
+                    let cmp_height = self.height(&Position { x: distance, y: position.y });
+                    if cmp_height >= target_height {
+                        return false;
+                    }
+                }
+            },
+            Direction::Right => {
+                for distance in (position.x + 1)..self.size {
+                    let cmp_height = self.height(&Position { x: distance, y: position.y });
+                    if cmp_height >= target_height {
+                        return false;
+                    }
+                }
+            },
+        }
+        true
+    }
+
+    fn distance(&self, start: &Position, direction: &Direction) -> usize {
+        let target_height = self.height(start);
+        let position = start.clone();
+        let mut distance = 0;
+
+        match direction {
+            Direction::Up => {
+                for i in (0..position.y).rev() {
+                    let cmp_height = self.height(&Position { x: position.x, y: i });
+                    distance += 1;
+                    if cmp_height >= target_height {
+                        break;
+                    }
+                }
+            },
+            Direction::Down => {
+                for i in (position.y + 1)..self.size {
+                    let cmp_height = self.height(&Position { x: position.x, y: i });
+                    distance += 1;
+                    if cmp_height >= target_height {
+                        break;
+                    }
+                }
+            },
+            Direction::Left => {
+                for i in (0..position.x).rev() {
+                    let cmp_height = self.height(&Position { x: i, y: position.y });
+                    distance += 1;
+                    if cmp_height >= target_height {
+                        break;
+                    }
+                }
+            },
+            Direction::Right => {
+                for i in (position.x + 1)..self.size {
+                    let cmp_height = self.height(&Position { x: i, y: position.y });
+                    distance += 1;
+                    if cmp_height >= target_height {
+                        break;
+                    }
+                }
+            },
+        }
+        distance
+    }
+}
+
+fn read_input<T: AsRef<Path>>(filename: T) -> Result<Trees> {
+    let reader = BufReader::new(File::open(filename)?);
+    let mut size = 0;
+
+    let heights = reader.lines().map(
+        |v| {
+            size += 1;
+            let s = v?;
+            s.bytes().map(|height| match height {
+                b'0'..=b'9' => Ok(height - b'0'),
+                _ => Err(anyhow!("Invalid digit: '{height}'")),
+            }).collect::<Result<Vec<_>>>()
+        }
+    ).collect::<Result<Vec<_>>>()?.into_iter().flatten().collect();
+
+    Trees::new_with_size(size, heights)
+}
+
+fn part1(input: &Trees) -> Result<usize> {
+    let mut positions: Vec<Position> = vec![];
+
+    for direction in [Direction::Up, Direction::Down, Direction::Left, Direction::Right].iter() {
+        for y in 0..input.size() {
+            for x in 0..input.size() {
+                let position = Position { x, y };
+                if input.is_visible(&position, *direction) && !positions.contains(&position) {
+                    positions.push(position);
+                }
+            }
+        }
+    }
+
+    Ok(positions.len())
+}
+
+fn part2(input: &Trees) -> Result<usize> {
+    (0..input.size()).flat_map(|y|
+        (0..input.size()).map(move |x| {
+            let position = Position { x, y };
+            [Direction::Up, Direction::Down, Direction::Left, Direction::Right].iter()
+            .map(|direction| {
+                input.distance(&position, direction)
+            }).product()
+        }
+    )).max().ok_or_else(|| anyhow!("Really, a tree patch with a 1-by-1 grid?"))
+}
+
+fn main() -> Result<()> {
+    let ( do_part_1, do_part_2 ) = aoc::do_parts();
+
+    let filename = args().nth(1).ok_or_else(|| anyhow!("Missing input filename"))?;
+    let input = read_input(filename).context("Could not read input")?;
+    if do_part_1 {
+        let solution = part1(&input).context("No solution for part 1")?;
+        println!("Part1, solution found to be: {}", solution);
+    }
+    if do_part_2 {
+        let solution = part2(&input).context("No solution for part 2")?;
+        println!("Part2, solution found to be: {}", solution);
+    }
+    Ok(())
+}