84 lines
2.7 KiB
Rust
84 lines
2.7 KiB
Rust
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use std::io::{self, BufRead};
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use std::fmt::Debug;
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fn main() {
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task1();
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task2();
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}
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// x = (T - t) * t = T * t - t^2
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// 0 = t^2 - T * t + x
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fn task1() {
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let input = "input.txt";
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let mut lines = read_lines(&input);
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let times = split_line(&lines.next().unwrap().expect("No line found"));
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let distances = split_line(&lines.next().unwrap().expect("No line found"));
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assert_eq!(times.len(), distances.len(), "uneqal array lengths");
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let mut total_ways_mult: i32 = 1;
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for i in 0..times.len() {
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let mut n_ways: i32 = 0;
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for t in 1..times[i] {
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let x: i32 = times[i] * t - t.pow(2);
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// println!("T={}, t={}, x={}", times[i], t, x);
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if x > distances[i] {
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n_ways += 1;
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}
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}
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total_ways_mult *= n_ways;
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}
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println!("Product of number of ways: {}", total_ways_mult);
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}
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fn task2() {
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let input = "input.txt";
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let mut lines = read_lines(&input);
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let time = parse2(&lines.next().unwrap().expect("No line found"));
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let distance = parse2(&lines.next().unwrap().expect("No line found"));
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// println!("time={}, distance={}", time, distance);
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let t1 = solve_squared(1., -time, distance, 1.);
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let t2 = solve_squared(1., -time, distance, -1.);
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// println!("t1={}, t2={}", t1, t2);
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let lower = t1.min(t2) as u64;
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let upper = t1.max(t2) as u64;
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// println!("lower={}, upper={}", lower, upper);
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println!("Number of possible ways: {}", upper-lower);
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// validation
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// let distance = |t: u64| (time as u64 - t) * t;
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// println!("distance(t1)={}, distance(t2)={}", distance(lower), distance(upper));
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}
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fn solve_squared(a: f64, b: f64, c: f64, sign: f64) -> f64 {
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return (-b + sign * (b * b - 4. * a * c).sqrt() as f64) / (2. * a);
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}
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fn parse2(line: &str) -> f64 {
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let l = rm_char(&line, ' ');
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// println!("{}", l);
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return l[l.find(':').unwrap()+1..].parse::<f64>().unwrap();
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}
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fn rm_char(original: &str, c: char) -> String {
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return original.chars().filter(|x| x != &c).collect();
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}
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fn split_line(line: &str) -> Vec<i32> {
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let colon = line.find(':').unwrap_or(0);
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return split_into_numbers::<i32>(&line[colon+2..]).collect();
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}
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fn split_into_numbers<T: std::str::FromStr>(x: &str) -> impl Iterator<Item = T> + '_ where <T as std::str::FromStr>::Err: Debug {
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return x.split(' ').filter(|&n| {n != "" && n != " "}).map(|n| n.parse::<T>().unwrap());
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}
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fn read_lines<P>(filename: P) -> io::Lines<io::BufReader<std::fs::File>>
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where P: AsRef<std::path::Path>, {
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return match std::fs::File::open(filename) {
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Err(why) => panic!("Could not open file. {}", why),
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Ok(file) => std::io::BufReader::new(file).lines()
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};
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}
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