day 6 part 2

src/bin/day6.rs

@@ -30,13 +30,7 @@ fn parser() -> impl Parser<char, Vec<Game>, Error = Simple<char>> {
 		.then_ignore(end())
 }
 
-fn main() -> anyhow::Result<()> {
-	let games = read("inputs/day6.txt", parser())?;
-
-	let mut result = 1;
-	for game in &games {
-		let t = game.time;
-		let d = game.distance + 1;
+fn ways2win(t: i64, d: i64) -> i64 {
 	// we want the minimum a s.t. (t-a)*a > d,
 	// and the maximum a s.t.     (t-a)*a < d
 	// that means we have a quadratic function -a² + ta - d and we want to find
@@ -44,7 +38,7 @@ fn main() -> anyhow::Result<()> {
 
 	let discriminant = t * t - 4 * d;
 	if discriminant < 0 {
-			continue;
+		return 0;
 	}
 	let sqrt = (discriminant as f64).sqrt();
 	let min = ((t as f64 - sqrt) / 2.0).ceil() as i64;
@@ -56,9 +50,28 @@ fn main() -> anyhow::Result<()> {
 	);
 	assert!(max >= min);
 
-		result *= max - min + 1;
+	max - min + 1
+}
+
+fn main() -> anyhow::Result<()> {
+	let games = read("inputs/day6.txt", parser())?;
+
+	println!(
+		"{}",
+		games
+			.iter()
+			.map(|game| ways2win(game.time, game.distance))
+			.product::<i64>()
+	);
+
+	let mut t = 0;
+	let mut d = 0;
+	for game in &games {
+		t = t * 10i64.pow((game.time as f64).log10().floor() as u32 + 1) + game.time;
+		d = d * 10i64.pow((game.distance as f64).log10().floor() as u32 + 1)
+			+ game.distance;
 	}
-	println!("{result}");
+	println!("{}", ways2win(t, d));
 
 	Ok(())
 }