day7/src/main.rs


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use std::fs;
use std::path::Path;

/* AOC21 Day 7: https://adventofcode.com/2021/day/7
 *
 * Some details about the solutions can be found here:
 *
 *  https://web.archive.org/web/20211208180308/https://cdn.discordapp.com/attachments/541932275068174359/917882191298592788/crab_submarines.pdf
 *
 */
fn main() {
    let input = Path::new("resources").join("input.txt");
    let content = fs::read_to_string(input).expect("Unable to read input file");
    let mut report: Vec<i32> = content.split(",").map(|x| x.parse().expect("Malformed input")).collect();
    report.sort();
    println!("Ex1: The result is {}", ex1(&report));
    println!("Ex1: The result is {}", ex2(&report));
}

fn ex1(report: &[i32]) -> i32 {
    let median = report[(report.len() as f32 / 2.).round() as usize];
    report.iter().fold(0, |a,x| a + (x-median).abs())
}

fn ex2(report: &[i32]) -> i32 {
    let mean = (report.iter().sum::<i32>() as f32 / report.len() as f32).floor() as i32;
    report.iter().fold(0, |a,x| { let d = (x-mean).abs(); a + (d*(d+1)/2) })
}