day06: rust

06/README.md

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+# [Day 6](https://adventofcode.com/2023/day/6) 
+:gift::gift::gift::gift::gift::gift:
+
+Today's language: **Rust**
+
+*Midnight formula go brrrrr*
+
+<!-- quadratic formula go *brrrr* -->
+
+```shell
+rustc day06.rs
+./day06
+```

06/day06.rs

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