2023/day09.rs


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use std::fs::File;
use std::io::Read;

fn diff(arr: &Vec<i64>) -> Vec<i64> {
    arr.iter()
        .zip(arr.iter().skip(1))
        .map(|(x, y)| y - x)
        .collect()
}

fn main() {
    // let filename = "in/day09.ref";
    let filename = "in/day09.pzl";

    let mut f = File::open(filename).expect("cannot open file");
    let mut content = String::new();
    f.read_to_string(&mut content).expect("cannot read file");
    let lines = content.trim_end().split('\n');
    // println!("{:?}", lines);

    let mut inp: Vec<Vec<i64>> = Vec::new();
    for line in lines {
        let l: Vec<i64> = line.split(' ').map(|x| x.parse().unwrap()).collect();
        inp.push(l);
    }

    let mut res1 = 0;
    let mut res2 = 0;

    for nums in inp.iter() {
        let mut desc: Vec<Vec<i64>> = Vec::new();
        desc.push(nums.clone());
        let mut d = diff(&nums);
        desc.push(d.clone());
        while d.iter().filter(|x| **x != 0).collect::<Vec<_>>().len() != 0 {
            d = diff(&d);
            desc.push(d.clone());
        }

        let mut a: i64 = *desc[desc.len() - 2].last().unwrap();
        for i in 0..desc.len() - 2 {
            a = *desc[desc.len() - 3 - i].last().unwrap() + a;
        }
        res1 += a;

        let mut b: i64 = desc[desc.len() - 2][0];
        for i in 0..desc.len() - 2 {
            b = desc[desc.len() - 3 - i][0] - b;
        }
        res2 += b;
    }

    println!("res1: {}", res1);
    println!("res2: {}", res2);
    assert_eq!(res1, 1938800261);
    assert_eq!(res2, 1112);
}