52 lines
1.3 KiB
Rust
52 lines
1.3 KiB
Rust
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use crate::prelude::*;
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pub fn solution() -> Solution {
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Solution::new(Day::new(10, 2020), part_1, part_2)
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.with_expected(2368, 1727094849536_i64)
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}
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fn parse_numbers(input: &str) -> (HashMap<usize, i32>, HashMap<i32, u32>) {
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let mut numbers = input
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.lines()
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.map(|line| line.parse().unwrap())
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.collect::<Vec<usize>>();
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numbers.push(0);
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numbers.sort_unstable();
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numbers.push(numbers.last().unwrap() + 3);
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let mut intervals = HashMap::new();
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let mut streaks = HashMap::new();
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let mut streak_length = 0;
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for (index, a) in numbers.iter().enumerate() {
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if let Some(b) = numbers.get(index + 1) {
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let interval = b - a;
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if interval == 1 {
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streak_length += 1;
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} else {
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*streaks.entry(streak_length).or_insert(0) += 1;
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streak_length = 0;
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}
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*intervals.entry(interval).or_insert(0) += 1;
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}
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}
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(intervals, streaks)
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}
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fn part_1(input: &str) -> Result<String> {
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let (intervals, _) = parse_numbers(input);
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Ok((intervals.get(&1).unwrap() * intervals.get(&3).unwrap()).to_string())
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}
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fn part_2(input: &str) -> Result<String> {
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let (_, streaks) = parse_numbers(input);
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Ok(
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(7_usize.pow(*streaks.get(&4).unwrap())
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* 4_usize.pow(*streaks.get(&3).unwrap())
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* 2_usize.pow(*streaks.get(&2).unwrap()))
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.to_string(),
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)
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}
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