2023 day6/rust: add solution

2023/day6/rust/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "rust_2023_06"
+version = "0.1.0"
+edition = "2021"
+
+# See more keys and their definitions at https://doc.rust-lang.org/cargo/reference/manifest.html
+
+[dependencies]
+aoc = { path = "../../../common/rust" }

2023/day6/rust/src/main.rs

@@ -0,0 +1,64 @@
+#![warn(clippy::pedantic)]
+
+use std::io::stdin;
+
+fn calculate_score<I: IntoIterator<Item = (u64, u64)>>(races: I) -> u64 {
+    races
+        .into_iter()
+        .map(|(t, r)| {
+            // x(t-x) = r
+            // tx-x^2 = r
+            // x^2-tx+r = 0
+            // [ x^2+px+q = 0  ==>  x = -p/2±sqrt((p/2)^2-q) ]
+            // x = t/2 ± sqrt(t^2/4-r)
+
+            #[allow(clippy::cast_precision_loss)]
+            let t = t as f64;
+            #[allow(clippy::cast_precision_loss)]
+            let r = r as f64;
+
+            let v = t / 2.0;
+            let w = (t.powi(2) / 4.0 - r).sqrt();
+            #[allow(clippy::cast_possible_truncation, clippy::cast_sign_loss)]
+            ((v - w + 1.0).floor() as u64, (v + w - 1.0).ceil() as u64)
+        })
+        .map(|(min, max)| max - min + 1)
+        .product()
+}
+
+fn make_races<F>(
+    times_line: &str,
+    records_line: &str,
+    make_numbers: F,
+) -> impl Iterator<Item = (u64, u64)>
+where
+    F: Fn(&[&str]) -> Vec<u64>,
+{
+    let do_line = |line: &str| {
+        let parts: Vec<_> = line.split(' ').filter(|s| !s.is_empty()).skip(1).collect();
+        make_numbers(&parts)
+    };
+
+    do_line(times_line).into_iter().zip(do_line(records_line))
+}
+
+fn main() {
+    let mut lines = stdin().lines().map(Result::unwrap);
+
+    let times = lines.next().unwrap();
+    let records = lines.next().unwrap();
+
+    println!(
+        "{}",
+        calculate_score(make_races(&times, &records, |parts| {
+            parts.iter().map(|n| n.parse().unwrap()).collect()
+        }))
+    );
+
+    println!(
+        "{}",
+        calculate_score(make_races(&times, &records, |parts| {
+            vec![parts.iter().copied().collect::<String>().parse().unwrap()]
+        }))
+    );
+}

Cargo.lock

@@ -677,6 +677,13 @@ dependencies = [
  "aoc",
 ]
 
+[[package]]
+name = "rust_2023_06"
+version = "0.1.0"
+dependencies = [
+ "aoc",
+]
+
 [[package]]
 name = "rustversion"
 version = "1.0.11"

Cargo.toml

@@ -31,4 +31,5 @@ members = [
 	"2023/day2/rust",
 	"2023/day4/rust",
 	"2023/day5/rust",
+	"2023/day6/rust",
 ]