Day 24: Never Tell Me The Odds (part 1)

README.md

@@ -28,4 +28,4 @@ Development occurs in language-specific directories:
 |[Day21.hs](hs/src/Day21.hs)|[Day21.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day21.kt)|[day21.py](py/aoc2023/day21.py)|[day21.rs](rs/src/day21.rs)|
 |[Day22.hs](hs/src/Day22.hs)|[Day22.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day22.kt)|[day22.py](py/aoc2023/day22.py)|[day22.rs](rs/src/day22.rs)|
 ||[Day23.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day23.kt)|||
-|[Day24.hs](hs/src/Day24.hs) ½|[Day24.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day24.kt) ½|[day24.py](py/aoc2023/day24.py) ½||
+|[Day24.hs](hs/src/Day24.hs) ½|[Day24.kt](kt/aoc2023-lib/src/commonMain/kotlin/com/github/ephemient/aoc2023/Day24.kt) ½|[day24.py](py/aoc2023/day24.py) ½|[day24.rs](rs/src/day24.rs) ½|

rs/benches/criterion.rs

@@ -1,6 +1,6 @@
 use aoc2023::{
     day1, day10, day11, day12, day13, day14, day15, day16, day17, day18, day19, day2, day20, day21,
-    day22, day3, day4, day5, day6, day7, day8, day9,
+    day22, day24, day3, day4, day5, day6, day7, day8, day9,
 };
 use criterion::{black_box, Criterion};
 use std::env;
@@ -149,6 +149,11 @@ fn aoc2023_bench(c: &mut Criterion) -> io::Result<()> {
     g.bench_function("part 2", |b| b.iter(|| day22::part2(black_box(&data))));
     g.finish();
 
+    let data = get_day_input(24)?;
+    let mut g = c.benchmark_group("day 24");
+    g.bench_function("part 1", |b| b.iter(|| day24::part1(black_box(&data))));
+    g.finish();
+
     Ok(())
 }
 

rs/src/day24.rs

@@ -0,0 +1,77 @@
+use std::cmp::Ordering;
+use std::ops::RangeInclusive;
+
+fn part1_internal(data: &str, lo: f64, hi: f64) -> Option<usize> {
+    let mut lines = Vec::<(f64, f64, RangeInclusive<f64>)>::new();
+    data.lines()
+        .map(|line| -> Option<usize> {
+            let (pos, vel) = line.split_once('@')?;
+            let mut iter = pos.splitn(3, ',');
+            let (x0, y0, _) = (
+                iter.next()?.trim().parse::<f64>().ok()?,
+                iter.next()?.trim().parse::<f64>().ok()?,
+                iter.next()?.trim().parse::<f64>().ok()?,
+            );
+            let mut iter = vel.splitn(3, ',');
+            let (vx0, vy0, _) = (
+                iter.next()?.trim().parse::<f64>().ok()?,
+                iter.next()?.trim().parse::<f64>().ok()?,
+                iter.next()?.trim().parse::<f64>().ok()?,
+            );
+            let m0 = vy0 / vx0;
+            let b0 = y0 - m0 * x0;
+            let range0 = match vx0.partial_cmp(&0.0)? {
+                Ordering::Less => -f64::INFINITY..=x0,
+                Ordering::Equal => return None,
+                Ordering::Greater => x0..=f64::INFINITY,
+            };
+            let n = lines
+                .iter()
+                .filter(|(m1, b1, range1)| {
+                    let x = (b0 - b1) / (m1 - m0);
+                    m0 != *m1
+                        && (lo..=hi).contains(&x)
+                        && (lo..=hi).contains(&(m0 * x + b0))
+                        && range0.contains(&x)
+                        && range1.contains(&x)
+                })
+                .count();
+            lines.push((m0, b0, range0));
+            Some(n)
+        })
+        .try_fold(0, |acc, n| Some(acc + n?))
+}
+
+pub fn part1(data: &str) -> Option<usize> {
+    part1_internal(data, 2e14, 4e14)
+}
+
+pub fn part2(_data: &str) -> Option<usize> {
+    None
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    use indoc::indoc;
+    use pretty_assertions::assert_eq;
+
+    static EXAMPLE: &str = indoc! {"
+        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 part1_examples() {
+        assert_eq!(Some(2), part1_internal(EXAMPLE, 7.0, 27.0));
+    }
+
+    #[test]
+    #[ignore]
+    fn part2_examples() {
+        assert_eq!(Some(47), part2(EXAMPLE));
+    }
+}

rs/src/lib.rs

@@ -13,6 +13,7 @@ pub mod day2;
 pub mod day20;
 pub mod day21;
 pub mod day22;
+pub mod day24;
 pub mod day3;
 pub mod day4;
 pub mod day5;

rs/src/main.rs

@@ -1,6 +1,6 @@
 use aoc2023::{
     day1, day10, day11, day12, day13, day14, day15, day16, day17, day18, day19, day2, day20, day21,
-    day22, day3, day4, day5, day6, day7, day8, day9,
+    day22, day24, day3, day4, day5, day6, day7, day8, day9,
 };
 use std::collections::HashSet;
 use std::env;
@@ -195,5 +195,12 @@ fn main() -> io::Result<()> {
         println!();
     }
 
+    if args.is_empty() || args.contains("24") {
+        println!("Day 24");
+        let data = get_day_input(24)?;
+        println!("{:?}", day24::part1(&data).expect("error"));
+        println!();
+    }
+
     Ok(())
 }