advent-of-code/aoc2020/src/day01.rs

105 lines
2.3 KiB
Rust

use std::collections::HashSet;
use std::fmt::Write;
use aoc::{err, Result};
const INPUT: &str = include_str!("../input/day01.txt");
pub fn run() -> Result<String> {
let mut res = String::with_capacity(128);
writeln!(res, "part 1: {}", part1(INPUT)?)?;
writeln!(res, "part 2: {}", part2(INPUT)?)?;
Ok(res)
}
fn part1(input: &str) -> Result<i64> {
let entries = input
.lines()
.map(|line| line.parse::<i64>().map_err(|e| err!("{}", e)))
.collect::<Result<Vec<i64>>>()?;
let (a, b) = find_2020_2_sum(&entries)?;
Ok(a * b)
}
fn part2(input: &str) -> Result<i64> {
let entries = input
.lines()
.map(|line| line.parse::<i64>().map_err(|e| err!("{}", e)))
.collect::<Result<Vec<i64>>>()?;
let (a, b, c) = find_2020_3_sum(&entries)?;
Ok(a * b * c)
}
fn find_2020_2_sum(entries: &[i64]) -> Result<(i64, i64)> {
for i in 0..entries.len() {
for j in 0..entries.len() {
if i == j {
continue;
}
if entries[i] + entries[j] == 2020 {
return Ok((entries[i], entries[j]));
}
}
}
Err(err!("couldn't find 2 elements that sum to 2020"))
}
fn find_2020_3_sum(entries: &[i64]) -> Result<(i64, i64, i64)> {
let set: HashSet<i64> = entries.iter().copied().collect();
for i in 0..entries.len() {
for j in 0..entries.len() {
if i == j {
continue;
}
let a = entries[i];
let b = entries[j];
let c = 2020 - a - b;
if set.contains(&c) {
return Ok((a, b, c));
}
}
}
Err(err!("couldn't find 2 elements that sum to 2020"))
}
#[cfg(test)]
mod tests {
use super::*;
static PROVIDED: &[i64] = &[1721, 979, 366, 299, 675, 1456];
#[test]
fn part1_provided() {
let (a, b) = find_2020_2_sum(PROVIDED).unwrap();
assert_eq!(a + b, 2020);
}
#[test]
fn part1_real() {
assert_eq!(part1(INPUT).unwrap(), 1014171);
}
#[test]
fn part2_provided() {
let (a, b, c) = find_2020_3_sum(PROVIDED).unwrap();
assert_eq!(a + b + c, 2020);
}
#[test]
fn part2_real() {
assert_eq!(part2(INPUT).unwrap(), 46584630);
}
}