Day 8

diff --git a/src/day08.rs b/src/day08.rs
new file mode 100644 (file)
index 0000000..013d55d
--- /dev/null
+++ b/src/day08.rs
@@ -0,0 +1,140 @@
+use itertools::{FoldWhile::{Continue, Done}, Itertools};
+
+#[derive(Clone, Copy)]
+enum Orientation {
+    West,
+    North,
+    Est,
+    South,
+}
+
+#[derive(Debug)]
+pub struct Matrix<T>(Vec<Vec<T>>);
+
+impl<T> Matrix<T>
+where
+    T: Default + Clone
+{
+    fn new(h: usize, w: usize) -> Self {
+        let mut m: Vec<Vec<T>> = Vec::new();
+        for _ in 0..h {
+            m.push(vec![T::default(); w]);
+        }
+        Matrix(m)
+    }
+
+    fn rotate(&self, i: usize, j: usize, o: Orientation) -> (usize, usize) {
+        match o {
+            Orientation::West => (i, j),
+            Orientation::North => (j, self.height() - i - 1),
+            Orientation::Est => (self.height() - i - 1, self.width() - j - 1),
+            Orientation::South => (self.width() - j - 1, i),
+        }
+    }
+
+    fn get(&self, i: usize, j: usize) -> &T {
+        &self.0[i][j]
+    }
+
+    fn get_orientation(&self, i: usize, j: usize, o: Orientation) -> &T {
+        let (i, j) = self.rotate(i, j, o);
+        &self.0[i][j]
+    }
+
+    fn set_orientation(&mut self, i: usize, j: usize, o: Orientation, value: T) {
+        let (i, j) = self.rotate(i, j, o);
+        self.0[i][j] = value;
+    }
+
+    fn height(&self) -> usize {
+        self.0.len()
+    }
+
+    fn width(&self) -> usize {
+        self.0[0].len()
+    }
+}
+
+
+pub fn parse(input: &str) -> Matrix<i32> {
+    let mut m: Vec<Vec<i32>> = Vec::new();
+    for l in input.lines() {
+        let row: Vec<i32> = l.trim().chars().map(|c| c.to_digit(10).unwrap() as i32).collect();
+        m.push(row);
+    }
+    Matrix(m)
+}
+
+// O(n).
+pub fn number_of_visible_trees(forest: &Matrix<i32>) -> i32 {
+    let h = forest.height();
+    let w = forest.width();
+
+    let mut visibility = Matrix::<bool>::new(h, w);
+    let mut nb_visible_tree = 0;
+
+    for o in [Orientation::West, Orientation::North, Orientation::Est, Orientation::South] {
+        for i in 0..h {
+            let mut max = -1;
+            for j in 0..w {
+                let tree_height = forest.get_orientation(i, j, o);
+                if *tree_height > max {
+                    if !visibility.get_orientation(i, j, o) {
+                        visibility.set_orientation(i, j, o, true);
+                        nb_visible_tree += 1
+                    }
+                    max = *tree_height;
+                }
+            }
+        }
+    }
+    nb_visible_tree
+}
+
+pub fn best_scenic_score(forest: &Matrix<i32>) -> i32 {
+    let h = forest.height();
+    let w = forest.width();
+
+    let mut current_best_score = -1;
+
+    for i in 1..h-1 {
+        for j in 1..w-1 {
+            let current = forest.get(i, j);
+            let dist_w = (1..j).rev().fold_while(1, |dist, j2| if forest.get(i, j2) >= current { Done(dist) } else { Continue(dist + 1) }).into_inner();
+            let dist_n = (1..i).rev().fold_while(1, |dist, i2| if forest.get(i2, j) >= current { Done(dist) } else { Continue(dist + 1) }).into_inner();
+            let dist_e = (j+1..w-1).fold_while(1, |dist, j2| if forest.get(i, j2) >= current { Done(dist) } else { Continue(dist + 1) }).into_inner();
+            let dist_s = (i+1..h-1).fold_while(1, |dist, i2| if forest.get(i2, j) >= current { Done(dist) } else { Continue(dist + 1) }).into_inner();
+
+            let score = dist_w * dist_n * dist_e * dist_s;
+            if score > current_best_score {
+                current_best_score = score;
+            }
+        }
+    }
+
+    current_best_score
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    static FOREST: &str =
+        "30373
+         25512
+         65332
+         33549
+         35390";
+
+    #[test]
+    fn part1() {
+        let forest = parse(FOREST);
+        assert_eq!(number_of_visible_trees(&forest), 21)
+    }
+
+    #[test]
+    fn part2() {
+        let forest = parse(FOREST);
+        assert_eq!(best_scenic_score(&forest), 8)
+    }
+}
\ No newline at end of file

diff --git a/src/main.rs b/src/main.rs
index cf08101..28b0f67 100644 (file)
--- a/src/main.rs
+++ b/src/main.rs
@@ -8,6 +8,7 @@ mod day04;
 mod day05;
 mod day06;
 mod day07;
+mod day08;
 
 fn day01() -> String {
     let f = fs::File::open("data/day01.input").unwrap();
@@ -64,6 +65,11 @@ fn day07() -> String {
     format!("part1: {}, part2: {}", sum_part1, min_part2)
 }
 
+fn day08() -> String {
+    let forest = day08::parse(&fs::read_to_string("data/day08.input").unwrap());
+    format!("part1: {}, part2: {}", day08::number_of_visible_trees(&forest), day08::best_scenic_score(&forest))
+}
+
 fn format_micros(t: u128) -> String {
     if t < 10_000 {
         format!("{} μs", t)
@@ -90,6 +96,7 @@ fn main() {
         day05,
         day06,
         day07,
+        day08,
     );
 
     let args: Vec<String> = env::args().skip(1).collect();