day 6 part 2
This commit is contained in:
parent
1d285ee38c
commit
146735881a
1 changed files with 37 additions and 24 deletions
|
@ -30,13 +30,7 @@ fn parser() -> impl Parser<char, Vec<Game>, Error = Simple<char>> {
|
||||||
.then_ignore(end())
|
.then_ignore(end())
|
||||||
}
|
}
|
||||||
|
|
||||||
fn main() -> anyhow::Result<()> {
|
fn ways2win(t: i64, d: i64) -> i64 {
|
||||||
let games = read("inputs/day6.txt", parser())?;
|
|
||||||
|
|
||||||
let mut result = 1;
|
|
||||||
for game in &games {
|
|
||||||
let t = game.time;
|
|
||||||
let d = game.distance + 1;
|
|
||||||
// we want the minimum a s.t. (t-a)*a > d,
|
// we want the minimum a s.t. (t-a)*a > d,
|
||||||
// and the maximum 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
|
// 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;
|
let discriminant = t * t - 4 * d;
|
||||||
if discriminant < 0 {
|
if discriminant < 0 {
|
||||||
continue;
|
return 0;
|
||||||
}
|
}
|
||||||
let sqrt = (discriminant as f64).sqrt();
|
let sqrt = (discriminant as f64).sqrt();
|
||||||
let min = ((t as f64 - sqrt) / 2.0).ceil() as i64;
|
let min = ((t as f64 - sqrt) / 2.0).ceil() as i64;
|
||||||
|
@ -56,9 +50,28 @@ fn main() -> anyhow::Result<()> {
|
||||||
);
|
);
|
||||||
assert!(max >= min);
|
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(())
|
Ok(())
|
||||||
}
|
}
|
||||||
|
|
Loading…
Reference in a new issue