use std::fs::File;
use std::io::prelude::*;

fn get_input() -> Vec<u8> {
    let mut file = File::open("input.txt").unwrap();
    let mut content = Vec::new();

    file.read_to_end(&mut content).unwrap();
    for i in 0 .. content.len() {
        content[i] = content[i] - ('0' as u8);
    }

    content
}

fn offset_sum(input: &[u8], offset: usize) -> i32 {
    let len = input.len();
    let mut sum = 0;

    for i in 0 .. len {
        let j = (i + offset) % len;
        if input[i] == input[j] {
            sum += input[i] as i32;
        }
    }

    sum
}

fn main() {
    let input = get_input();

    println!("Part 1 total: {}", offset_sum(&input, 1));
    println!("Part 2 total: {}", offset_sum(&input, input.len()/2));
}

$ ./program <input.txt

$ ./program $(cat input.txt)