67 lines
1.4 KiB
Rust
67 lines
1.4 KiB
Rust
use aoc_runner_derive::{aoc, aoc_generator};
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type Data = Vec<usize>;
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#[derive(Debug, Clone)]
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enum Seen {
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Never,
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Once(usize),
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Twice(usize, usize),
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}
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impl Default for Seen {
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fn default() -> Self {
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Seen::Never
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}
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}
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impl Seen {
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fn add(&mut self, n: usize) -> usize {
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*self = match self {
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Self::Never => Self::Once(n),
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Self::Once(i) => Self::Twice(*i, n),
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Self::Twice(_, i) => Self::Twice(*i, n),
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};
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return self.diff();
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}
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fn diff(&self) -> usize {
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match self {
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Seen::Never => unreachable!(),
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Seen::Once(_) => 0,
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Seen::Twice(a, b) => b - a,
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}
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}
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}
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#[aoc_generator(day15)]
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pub fn input_generator(input: &str) -> Data {
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input
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.split(',')
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.map(|num| num.parse())
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.collect::<Result<Vec<usize>, _>>()
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.unwrap()
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}
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fn get_number(start: &[usize], num_turns: usize) -> usize {
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let mut cache = vec![Seen::Never; num_turns];
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let mut nums = start.to_vec();
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let mut num = std::usize::MAX;
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for i in 1..num_turns {
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num = cache[nums[i - 1]].add(i);
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if i >= nums.len() {
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nums.push(num);
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}
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}
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return num;
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}
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#[aoc(day15, part1)]
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pub fn solve_part1(input: &[usize]) -> usize {
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return get_number(input, 2020);
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}
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#[aoc(day15, part2)]
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pub fn solve_part2(input: &[usize]) -> usize {
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return get_number(input, 30_000_000);
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}
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