Solve 09.1

src/bin/09.rs

@@ -0,0 +1,132 @@
+use aoc::*;
+use derive_more::Deref;
+use glam::U64Vec2;
+use itertools::Itertools;
+use std::ops::Sub;
+
+const INPUT: &str = include_str!("../../input/09");
+
+fn main() {
+    println!("Part 1: {}", part1(INPUT));
+    println!("Part 2: {}", part2(INPUT));
+}
+
+#[test]
+fn example() {
+    assert_example!(part1, "09-test", 50);
+    assert!(Line(U64Vec2::new(0, 10), U64Vec2::ZERO).contains(U64Vec2::new(0, 0)));
+    assert!(Line(U64Vec2::new(0, 10), U64Vec2::ZERO).contains(U64Vec2::new(0, 10)));
+    assert!(!Line(U64Vec2::new(0, 10), U64Vec2::ZERO).contains(U64Vec2::new(0, 11)));
+    assert!(!Line(U64Vec2::new(0, 10), U64Vec2::ZERO).contains(U64Vec2::new(1, 10)));
+    assert_example!(part2, "09-test", 24);
+}
+
+fn part1(input: &str) -> u64 {
+    Polygon::parse(input)
+        .0
+        .into_iter()
+        .tuple_combinations()
+        .map(Rect::from)
+        .map(Rect::area)
+        .max()
+        .unwrap()
+}
+
+fn part2(input: &str) -> u64 {
+    let polygon = Polygon::parse(input);
+    polygon
+        .iter()
+        .copied()
+        .tuple_combinations()
+        .map(Rect::from)
+        .filter(|&r| polygon.contains_rect(r))
+        .map(Rect::area)
+        .max()
+        .unwrap()
+}
+
+#[derive(Deref)]
+struct Polygon(Vec<U64Vec2>);
+
+impl Polygon {
+    fn parse(input: &str) -> Self {
+        Self(input.lines().map(parse_line).collect())
+    }
+
+    fn contains_rect(&self, r: Rect) -> bool {
+        r.all_points().into_iter().all(|p| self.contains_point(p))
+    }
+
+    /// Raycast from left to right and check intersections with lines.
+    fn contains_point(&self, p: U64Vec2) -> bool {
+        let lines = self.lines();
+        let is_on_line = |p| lines.iter().any(|line| line.contains(p));
+
+        let mut inside = false;
+        let mut was_on_line = false;
+
+        for x in 0..=p.x {
+            let check = U64Vec2::new(x, p.y);
+            let is_on_line = is_on_line(check);
+            let crossed = !is_on_line && was_on_line;
+            if crossed {
+                inside ^= true;
+            }
+            was_on_line = is_on_line;
+        }
+
+        inside || was_on_line
+    }
+
+    fn lines(&self) -> Vec<Line> {
+        self.iter()
+            .chain(self.first()) // close the loop
+            .copied()
+            .tuple_combinations()
+            .map(|(a, b)| Line(a, b))
+            .collect()
+    }
+}
+
+#[derive(Clone, Copy)]
+struct Line(U64Vec2, U64Vec2);
+
+impl Line {
+    /// true if p on Line(a, b)
+    fn contains(&self, p: U64Vec2) -> bool {
+        let a = self.0.sub(p).length_squared();
+        let b = self.1.sub(p).length_squared();
+        let c = self.0.sub(self.1).length_squared();
+        a + b == c
+    }
+}
+
+#[derive(Copy, Clone)]
+struct Rect(U64Vec2, U64Vec2);
+
+impl Rect {
+    fn area(self) -> u64 {
+        (self.0.x.abs_diff(self.1.x) + 1) * (self.0.y.abs_diff(self.1.y) + 1)
+    }
+
+    fn from((a, b): (U64Vec2, U64Vec2)) -> Self {
+        Self(a, b)
+    }
+
+    fn all_points(self) -> Vec<U64Vec2> {
+        let mut result = Vec::new();
+
+        for x in self.0.x.min(self.1.x)..=self.0.x.max(self.1.x) {
+            for y in self.0.y.min(self.1.y)..=self.0.y.max(self.1.y) {
+                result.push(U64Vec2::new(x, y));
+            }
+        }
+
+        result
+    }
+}
+
+fn parse_line(line: &str) -> U64Vec2 {
+    let (x, y) = line.split_once(',').unwrap();
+    U64Vec2::new(x.parse().unwrap(), y.parse().unwrap())
+}