adventofcode-2021-day1

use aoc_runner_derive::{aoc, aoc_generator, aoc_lib};
use std::error::Error;

#[aoc_generator(day1)]
fn parse_input(input: &str) -> Result<Vec<usize>, Box<dyn Error>> {
    Ok(input
        .lines()
        .map(|line| line.parse::<usize>().unwrap())
        .collect())
}

fn count_increases(input: Vec<usize>) -> usize {
    input
        .iter()
        .fold((usize::MAX, 0), |(prev, sum), &val| {
            (val, sum + if val > prev { 1 } else { 0 })
        })
        .1
}

#[aoc(day1, part1)]
pub fn solve_part1(input: &[usize]) -> usize {
    count_increases(Vec::from(input))
}

#[aoc(day1, part2)]
pub fn solve_part2(input: &[usize]) -> usize {
    let measures = (0..input.len() - 2)
        .map(|i| input[i..i + 3].iter().sum())
        .collect();
    count_increases(measures)
}

aoc_lib! { year = 2021 }