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use std::marker::PhantomData;
#[derive(Debug)]
struct Race<Part = One> {
times: Vec<u64>,
distances: Vec<u64>,
state: std::marker::PhantomData<Part>,
}
struct One;
struct Two;
impl From<&str> for Race<One> {
fn from(value: &str) -> Self {
let (times, distances) = value.split_once("\n").unwrap();
let (_, times) = times.split_once(':').unwrap();
let (_, distances) = distances.split_once(':').unwrap();
let times = times
.split_whitespace()
.map(|x| x.parse::<u64>().unwrap())
.collect::<Vec<_>>();
let distances = distances
.split_whitespace()
.map(|x| x.parse::<u64>().unwrap())
.collect::<Vec<_>>();
Self {
times,
distances,
state: PhantomData::<One>,
}
}
}
impl From<&str> for Race<Two> {
fn from(value: &str) -> Self {
let (times, distances) = value.split_once("\n").unwrap();
let (_, times) = times.split_once(':').unwrap();
let (_, distances) = distances.split_once(':').unwrap();
let times = times
.chars()
.filter(|ch| ch.is_digit(10))
.collect::<String>()
.parse::<u64>()
.unwrap();
let distances = distances
.chars()
.filter(|ch| ch.is_digit(10))
.collect::<String>()
.parse::<u64>()
.unwrap();
Self {
times: vec![times],
distances: vec![distances],
state: PhantomData::<Two>,
}
}
}
fn quadratic_equation(a: f64, b: f64, c: f64) -> (f64, f64) {
let discriminant = b * b - 4.0 * a * c;
let root1 = (-b - discriminant.sqrt()) / (2.0 * a);
let root2 = (-b + discriminant.sqrt()) / (2.0 * a);
// hacky solution to round the first root up and the scond root down
((root1 + 0.52).round(), (root2 - 0.52).round())
}
fn solve_math_two(data: &str) -> u64 {
let race: Race<Two> = Race::from(data);
race.times
.iter()
.zip(race.distances.iter())
.map(|(&time, &distance)| {
let (start, end) = quadratic_equation(1.0, -((time - 0) as f64), distance as f64);
(end - start + 1.0) as usize
})
.product::<usize>() as u64
}
fn solve_math_one(data: &str) -> u64 {
let race: Race<One> = Race::from(data);
race.times
.iter()
.zip(race.distances.iter())
.map(|(&time, &distance)| {
let (start, end) = quadratic_equation(1.0, -((time - 0) as f64), distance as f64);
(end - start + 1.0) as usize
})
.product::<usize>() as u64
}
fn solve_part_one(data: &str) -> u64 {
let race: Race<One> = Race::from(data);
race.times
.iter()
.zip(race.distances.iter())
.map(|(&time, &distance)| {
(0..time)
.into_iter()
.filter(|t| (time - t) * t > distance)
.map(|_| distance)
.count()
})
.product::<usize>() as u64
}
fn solve_part_two(data: &str) -> u64 {
let race: Race<Two> = Race::from(data);
race.times
.iter()
.zip(race.distances.iter())
.map(|(&time, &distance)| {
(0..time)
.into_iter()
.filter(|t| (time - t) * t > distance)
.map(|_| distance)
.count()
})
.product::<usize>() as u64
}
fn main() {
let test = include_str!("../input/day6.test");
let prod = include_str!("../input/day6.prod");
println!("part_1 test: {:?}", solve_math_one(test));
println!("part_1 prod {:?}", solve_math_one(prod));
println!("part_2 test: {:?}", solve_math_two(test));
println!("part_2 prod {:?}", solve_math_two(prod));
}
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