advent-of-code-2024/day7/src/main.rs

use std::{env, fs};

fn read_input(path: &str) -> String {
    fs::read_to_string(path).expect("Cannot read file.")
}

fn add(a: u64, b: u64) -> u64 {
    a + b
}

fn mul(a: u64, b: u64) -> u64 {
    a * b
}

fn concat(a: u64, b: u64) -> u64 {
    format!("{a}{b}").parse().unwrap()
}

fn parse_input(input: &str) -> Vec<(u64, Vec<u64>)> {
    input
        .lines()
        .filter(|line| !line.is_empty())
        .map(|line| {
            let split_line = line.split_once(": ").unwrap();
            (
                split_line.0.parse().unwrap(),
                split_line
                    .1
                    .split_whitespace()
                    .map(|s| s.parse().unwrap())
                    .rev()
                    .collect(),
            )
        })
        .collect()
}

fn is_valid(
    data: &mut Vec<u64>,
    acc: u64,
    target: u64,
    operators: &Vec<&fn(u64, u64) -> u64>,
) -> bool {
    if data.is_empty() {
        return target == acc;
    }

    if acc > target {
        return false;
    }

    let old = data.pop().unwrap();
    for operator in operators {
        if is_valid(data, operator(acc, old), target, operators) {
            return true;
        }
    }
    data.push(old);
    false
}

fn sum_valid(
    calibration_data: &Vec<(u64, Vec<u64>)>,
    operators: &Vec<&fn(u64, u64) -> u64>,
) -> u64 {
    let mut sum_valid = 0;
    let calibration_data = calibration_data.clone();

    for calibration in calibration_data {
        let mut x = calibration.1;
        let acc = x.pop().unwrap();
        if is_valid(&mut x, acc, calibration.0, operators) {
            sum_valid += calibration.0;
        }
    }

    sum_valid
}

fn part_1(input: &Vec<(u64, Vec<u64>)>) -> u64 {
    let valid_operators = vec![&(add as fn(u64, u64) -> u64), &(mul as fn(u64, u64) -> u64)];

    sum_valid(input, &valid_operators)
}

fn part_2(input: &Vec<(u64, Vec<u64>)>) -> u64 {
    let valid_operators = vec![
        &(add as fn(u64, u64) -> u64),
        &(mul as fn(u64, u64) -> u64),
        &(concat as fn(u64, u64) -> u64),
    ];

    sum_valid(input, &valid_operators)
}

fn main() {
    let args: Vec<String> = env::args().collect();
    for arg in args.iter().skip(1) {
        let input = read_input(&arg);
        let calibration_data = parse_input(&input);
        println!("[{}]", &arg);
        println!("\t[Part 1] => Answer is '{}'.", part_1(&calibration_data));
        println!("\t[Part 2] => Answer is '{}'.", part_2(&calibration_data));
    }
}