95 lines
1.5 KiB
Rust
95 lines
1.5 KiB
Rust
#![feature(test)]
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extern crate test;
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use aoc2020::common::*;
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use itertools::Itertools;
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type Parsed = Vec<usize>;
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const STEP_SIZE: usize = 3;
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fn read_input() -> String {
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read_file(10)
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}
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fn parse_input(raw: &str) -> Parsed {
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let mut xs: Vec<usize> = raw.lines().map(|l| l.parse().unwrap()).collect();
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xs.push(0);
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// faster than using sorted() directly on the iterator
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xs.sort_unstable();
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xs
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}
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fn part1(input: &Parsed) -> (usize, usize) {
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input.iter().tuple_windows().fold((0, 1), |(one, three), (a, b)| match b - a {
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1 => (one + 1, three),
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2 => (one, three),
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3 => (one, three + 1),
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_ => unreachable!(),
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})
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}
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fn part2(input: &Parsed) -> usize {
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let mut iter = input.iter().rev();
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let max = *iter.next().unwrap();
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let mut paths = vec![0; max + STEP_SIZE];
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paths[max] = 1;
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for &i in iter {
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paths[i] = (1..=STEP_SIZE).map(|j| paths[i + j]).sum();
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}
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paths[0]
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}
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fn main() {
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let input = parse_input(&read_input());
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let (ones, threes) = part1(&input);
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println!("Part 1: {}", ones * threes);
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println!("Part 2: {}", part2(&input));
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}
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#[cfg(test)]
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mod tests {
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use super::*;
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use aoc2020::*;
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use paste::paste;
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use test::black_box;
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const TEST_INPUT: &str = "28
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33
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18
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42
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31
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14
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46
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20
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48
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47
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24
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23
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49
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45
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19
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38
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39
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11
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1
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32
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25
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35
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8
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17
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7
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9
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4
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2
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34
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10
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3";
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test!(part1() == (22, 10));
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test!(part2() == 19208);
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bench!(part1() == (69, 24));
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bench!(part2() == 56693912375296);
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bench_input!(len == 93);
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}
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