advent-of-code/source/year_2020/day_01/mod.rs

//! Day 01 of 2020.

use crate::prelude::*;

/// Get the solution for day 01 of 2020.
pub fn solution() -> Solution {
  Solution::new(Day::new(1, 2020), part_1, part_2)
    .with_expected(605364, 128397680)
}

/// The target sum that two entries need to add up to.
const TARGET: i32 = 2020;

/// Parse the input lines into integers.
fn parse_lines(input: &str) -> Vec<i32> {
  input
    .lines()
    .filter_map(|line| line.parse::<i32>().ok())
    .collect()
}

/// The logic to solve part one.
fn part_1(input: &str) -> Result<String> {
  Ok(
    parse_lines(input)
      .into_iter()
      .tuple_combinations()
      .find(|(a, b)| a + b == TARGET)
      .map(|(a, b)| a * b)
      .unwrap()
      .to_string(),
  )
}

/// The logic to solve part two.
fn part_2(input: &str) -> Result<String> {
  Ok(
    parse_lines(input)
      .into_iter()
      .tuple_combinations()
      .find(|(a, b, c)| a + b + c == TARGET)
      .map(|(a, b, c)| a * b * c)
      .unwrap()
      .to_string(),
  )
}