day24: problem 1 solution

24/Cargo.lock

@@ -0,0 +1,134 @@
+# This file is automatically @generated by Cargo.
+# It is not intended for manual editing.
+version = 3
+
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+dependencies = [
+ "memchr",
+]
+
+[[package]]
+name = "day24"
+version = "0.1.0"
+dependencies = [
+ "itertools",
+ "lazy-regex",
+]
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+ "regex-syntax",
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+ "quote",
+ "unicode-ident",
+]
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24/Cargo.toml

@@ -0,0 +1,10 @@
+[package]
+name = "day24"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+itertools = "0.12.0"
+lazy-regex = "3.1.0"

24/src/main.rs

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+use itertools::Itertools;
+use std::fmt::Debug;
+use std::fs::File;
+use std::io::{BufRead, BufReader, Lines};
+use std::ops::Index;
+use std::time::Instant;
+
+// BOILERPLATE
+type InputIter = Lines<BufReader<File>>;
+
+fn get_input() -> InputIter {
+    let f = File::open("input").unwrap();
+    let br = BufReader::new(f);
+    br.lines()
+}
+
+fn main() {
+    let start = Instant::now();
+    let ans1 = problem1(get_input());
+    let duration = start.elapsed();
+    println!("Problem 1 solution: {} [{}s]", ans1, duration.as_secs_f64());
+
+    let start = Instant::now();
+    let ans2 = problem2(get_input());
+    let duration = start.elapsed();
+    println!("Problem 2 solution: {} [{}s]", ans2, duration.as_secs_f64());
+}
+
+// Parse
+
+#[derive(Clone, Copy)]
+struct Vec3 {
+    x: f64,
+    y: f64,
+    z: f64,
+}
+impl Debug for Vec3 {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}, {}, {}", self.x, self.y, self.z)
+    }
+}
+
+#[derive(Clone, Copy)]
+struct Vec2 {
+    x: f64,
+    y: f64,
+}
+impl Debug for Vec2 {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{}, {}", self.x, self.y)
+    }
+}
+
+
+#[derive(Clone)]
+
+struct Hailstone {
+    pos: Vec3,
+    vel: Vec3,
+}
+
+impl Hailstone {
+    fn xy_vel_angle(&self) -> f64 {
+        (self.vel.y / self.vel.x).atan()
+    }
+    fn xy_vel_abs(&self) -> f64 {
+        (self.vel.x.powi(2) + self.vel.y.powi(2)).sqrt()
+    }
+    fn xy_slope(&self) -> f64 {
+        self.vel.y / self.vel.x
+    }
+    fn y_crossing(&self) -> f64 {
+        self.pos.y - self.xy_slope() * self.pos.x
+    }
+    fn xy_poi(&self, other: &Hailstone) -> Option<Vec2> {
+        let our_slope = self.xy_slope();
+        let other_slope = other.xy_slope();
+        if our_slope == other_slope || our_slope * other_slope == -1. {
+            None
+        } else {
+            let our_yint = self.y_crossing();
+            let other_yint = other.y_crossing();
+            let ratio = (other_yint - our_yint) / (our_slope - other_slope);
+            Some(Vec2 {
+                x: ratio,
+                y: our_slope * ratio + our_yint,
+            })
+        }
+    }
+    fn xy_point_future(&self, point: &Vec2) -> bool {
+        // a point will be in the past if the difference between its 'new' position and its 'start' position has a
+        // different sign than the velocity for any component
+        let diffs = [point.x - self.pos.x, point.y - self.pos.y];
+        // for (diff, vel) in diffs.iter().zip([self.vel.x, self.vel.y].iter()) {
+        //     println!(" diff: {:?} vel: {:?} mul: {:?}", diff, vel, diff * vel > 0.);
+        // }
+        diffs.iter().zip([self.vel.x, self.vel.y].iter()).any(|(diff, vel)| diff * vel > 0.)
+    }
+}
+
+impl From<&str> for Hailstone {
+    fn from(value: &str) -> Self {
+        let (pos, vel) = value.split_once("@").unwrap();
+        let [px, py, pz] = pos.split(",").map(|s| s.trim().parse::<f64>().unwrap()).collect_vec()[..] else {
+            panic!()
+        };
+        let [vx, vy, vz] = vel.split(",").map(|s| s.trim().parse::<f64>().unwrap()).collect_vec()[..] else {
+            panic!()
+        };
+
+        Self {
+            pos: Vec3 { x: px, y: py, z: pz },
+            vel: Vec3 { x: vx, y: vy, z: vz },
+        }
+    }
+}
+
+impl Debug for Hailstone {
+    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+        write!(f, "{:?} @ {:?}", self.pos, self.vel)
+    }
+}
+
+#[derive(Debug)]
+struct Hailstones {
+    stones: Vec<Hailstone>,
+}
+
+impl Hailstones {
+    fn count_xy_pois(&self, bounds: (f64, f64)) -> u64 {
+        assert!(bounds.0 < bounds.1);
+        let mut stones = self.stones.clone();
+
+        let mut count = 0;
+        while let Some(stone) = &stones.pop() {
+            for other in &stones {
+                let Some(poi) = stone.xy_poi(other) else { continue };
+                // println!("intersection: {:?} / {:?} @ {:?}", stone, other, poi);
+                if poi.x >= bounds.0 && poi.x <= bounds.1 && poi.y >= bounds.0 && poi.y <= bounds.1 && stone.xy_point_future(&poi) && other.xy_point_future(&poi) {
+                    count += 1;
+                }
+            }
+        }
+        
+        count
+    }
+}
+
+impl Index<usize> for Hailstones {
+    type Output = Hailstone;
+    fn index(&self, index: usize) -> &Self::Output {
+        &self.stones[index]
+    }
+}
+
+impl<T: BufRead> From<Lines<T>> for Hailstones {
+    fn from(value: Lines<T>) -> Self {
+        let mut stones = Vec::new();
+        for line in value {
+            stones.push(Hailstone::from(line.unwrap().as_str()));
+        }
+        Hailstones { stones }
+    }
+}
+
+// PROBLEM 1 solution
+
+fn problem1<T: BufRead>(input: Lines<T>) -> u64 {
+    problem1_impl(input, (200000000000000., 400000000000000.))
+}
+
+fn problem1_impl<T: BufRead>(input: Lines<T>, bounds: (f64, f64)) -> u64 {
+    let stones = Hailstones::from(input);
+
+    stones.count_xy_pois(bounds)
+}
+
+// PROBLEM 2 solution
+fn problem2<T: BufRead>(input: Lines<T>) -> u64 {
+    0
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::*;
+    use std::io::Cursor;
+
+    const EXAMPLE: &str = &"19, 13, 30 @ -2,  1, -2
+18, 19, 22 @ -1, -1, -2
+20, 25, 34 @ -2, -2, -4
+12, 31, 28 @ -1, -2, -1
+20, 19, 15 @  1, -5, -3";
+
+    #[test]
+    fn problem1_example() {
+        let c = Cursor::new(EXAMPLE);
+        assert_eq!(problem1_impl(c.lines(), (7., 27.)), 2);
+    }
+
+    #[test]
+    fn problem2_example() {
+        let c = Cursor::new(EXAMPLE);
+        assert_eq!(problem2(c.lines()), 0);
+    }
+}