2022/src/bin/day01.rs

use aoc_2022::file_to_lines;

use tracing::*;
use tracing_subscriber::EnvFilter;

use std::cmp::max;

struct Accum {
    max_sum: i32,
    current_sum: i32,
}

impl Accum {
    fn new() -> Accum {
        Accum {
            max_sum: 0,
            current_sum: 0,
        }
    }
}

fn part_1(input: &[i32]) -> i32 {
    input
        .iter()
        .fold(Accum::new(), |a, &x| {
            if x == -1 {
                Accum {
                    max_sum: max(a.max_sum, a.current_sum),
                    current_sum: 0,
                }
            } else {
                Accum {
                    max_sum: a.max_sum,
                    current_sum: a.current_sum + x,
                }
            }
        })
        .max_sum
}

fn part_2(input: &[i32]) -> i32 {
    let mut calories: Vec<i32> = Vec::new();

    let last_elf = input
        .iter()
        .fold(Accum::new(), |a, &x| {
            if x == -1 {
                calories.push(a.current_sum);
                Accum::new()
            } else {
                Accum {
                    max_sum: a.max_sum,
                    current_sum: a.current_sum + x,
                }
            }
        })
        .current_sum;
    calories.push(last_elf);

    calories.sort();
    calories.iter().rev().take(3).sum()
}

fn parse_input(pathname: &str) -> Vec<i32> {
    file_to_lines(pathname)
        .iter()
        .map(|s| if s.is_empty() { -1 } else { s.parse().unwrap() })
        .collect()
}

fn main() {
    tracing_subscriber::fmt()
        .with_env_filter(EnvFilter::from_default_env())
        .with_target(false)
        .with_file(true)
        .with_line_number(true)
        .without_time()
        .compact()
        .init();

    let input = parse_input("inputs/day01.txt");

    info!("Part 1: {}", part_1(&input));
    info!("Part 2: {}", part_2(&input));
}

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_part_1() {
        let sample = parse_input("samples/day01.txt");
        assert_eq!(part_1(&sample), 24000);
    }

    #[test]
    fn test_part_2() {
        let sample = parse_input("samples/day01.txt");
        assert_eq!(part_2(&sample), 45000);
    }
}