advent-of-code/2020/src/bin/day10.rs

126 lines
2.3 KiB
Rust
Raw Normal View History

2020-12-10 10:56:13 +01:00
#![feature(test)]
extern crate test;
use std::{env, iter};
use itertools::Itertools;
type Parsed = Vec<usize>;
fn read_input() -> String {
std::fs::read_to_string(
env::args()
.nth(1)
.filter(|n| n != "--bench")
.unwrap_or(String::from("inputs/day10")),
)
.unwrap()
}
fn parse_input(raw: &str) -> Parsed {
let mut xs: Vec<usize> = raw.lines().map(|l| l.parse().unwrap()).collect();
// faster than using sorted() directly on the iterator
xs.sort_unstable();
xs
}
fn part1(input: &Parsed) -> (usize, usize) {
iter::once(&0)
.chain(input.iter())
.tuple_windows()
.fold((0, 1), |(one, three), (a, b)| match b - a {
1 => (one + 1, three),
2 => (one, three),
3 => (one, three + 1),
_ => unreachable!(),
})
}
fn part2(input: &Parsed) -> usize {
let max = *input.last().unwrap();
let mut paths = vec![0; max + 4];
paths[max] = 1;
for i in input.iter().rev().skip(1) {
let mut n = 0;
for j in 1..=3 {
n += paths[i + j];
}
paths[*i] = n;
}
paths[1] + paths[2] + paths[3]
}
fn main() {
let input = parse_input(&read_input());
let (ones, threes) = part1(&input);
println!("Part 1: {}", ones * threes);
println!("Part 2: {}", part2(&input));
}
#[cfg(test)]
mod tests {
use super::*;
use test::black_box;
const TEST_INPUT: &str = "28
33
18
42
31
14
46
20
48
47
24
23
49
45
19
38
39
11
1
32
25
35
8
17
7
9
4
2
34
10
3";
#[test]
fn part1_test() {
let input = parse_input(TEST_INPUT);
assert_eq!(part1(&input), (22, 10));
}
#[test]
fn part2_test() {
let input = parse_input(TEST_INPUT);
assert_eq!(part2(&input), 19208);
}
#[bench]
fn bench_input_parsing(b: &mut test::Bencher) {
let raw = read_input();
b.iter(|| parse_input(black_box(&raw)))
}
#[bench]
fn bench_part1(b: &mut test::Bencher) {
let input = parse_input(&read_input());
b.iter(|| assert_eq!(part1(black_box(&input)), (69, 24)));
}
#[bench]
fn bench_part2(b: &mut test::Bencher) {
let input = parse_input(&read_input());
b.iter(|| assert_eq!(part2(black_box(&input)), 56693912375296));
}
}