adventofcode2023/day9/src/main.rs

use std::fs::read_to_string;

fn get_numbers_in_line_iter<T: std::str::FromStr>(str: &str) -> impl Iterator<Item=T> + '_ {
    str.split_whitespace().filter_map(|substr| substr.parse::<T>().ok())
}

fn main() {
    let mut sum1 = 0;
    let mut sum2 = 0;
    let mut working_vec: Vec<i32> = Vec::new();
    for line in read_to_string("input.txt").unwrap().lines() {
        working_vec.extend(get_numbers_in_line_iter::<i32>(line));
        let mut extrapolated1 = 0;
        let mut extrapolated2 = 0;
        let mut sequence_length = working_vec.len() - 1;
        while sequence_length > 0 {
            let mut all_zeros = true;
            // accumulate last element for task 1
            extrapolated1 += working_vec[sequence_length];
            // accumulate first element with subtraction for task 2
            extrapolated2 = working_vec[0] - extrapolated2;
            for i in 0..sequence_length {
                working_vec[i] = working_vec[i + 1] - working_vec[i];
                if working_vec[i] != 0 {
                    all_zeros = false;
                }
            }
            if all_zeros {
                break;
            }
            sequence_length -= 1;
        }
        // flip sign if there was an even amount of elements to account for processing it in reverse
        if (working_vec.len() - sequence_length) % 2 == 0 {
            extrapolated2 = -extrapolated2;
        }
        sum1 += extrapolated1;
        sum2 += extrapolated2;
        working_vec.clear();
    }
    println!("Sum1: {}", sum1);
    println!("Sum2: {}", sum2);
}