67 lines
1.4 KiB
Rust
67 lines
1.4 KiB
Rust
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#![allow(clippy::needless_range_loop)]
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#![forbid(elided_lifetimes_in_paths, unsafe_code)]
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use aoc23::read;
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use chumsky::{prelude::*, text::int};
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struct History(Vec<i64>);
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impl History {
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fn parser() -> impl Parser<char, Self, Error = Simple<char>> {
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one_of(['-', '0', '1', '2', '3', '4', '5', '6', '7', '8', '9'])
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.repeated()
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.at_least(1)
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.separated_by(just(" "))
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.map(|nums: Vec<Vec<char>>| {
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Self(
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nums.into_iter()
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.map(|num| num.into_iter().collect::<String>().parse().unwrap())
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.collect()
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)
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})
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}
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}
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fn parser() -> impl Parser<char, Vec<History>, Error = Simple<char>> {
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History::parser()
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.then_ignore(just("\n"))
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.repeated()
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.then_ignore(end())
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}
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impl History {
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fn diff(&self) -> Self {
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// intentionally reserve one space extra for .extend()
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let mut diffs = Vec::with_capacity(self.0.len());
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if self.0.len() > 1 {
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for i in 1 .. self.0.len() {
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diffs.push(self.0[i] - self.0[i - 1]);
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}
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}
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Self(diffs)
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}
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fn extend(&mut self) {
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if self.0.iter().any(|num| *num != 0) {
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let mut diff = self.diff();
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diff.extend();
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self.0.push(self.0.last().unwrap() + diff.0.last().unwrap());
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} else {
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self.0.push(0);
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}
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}
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}
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fn main() -> anyhow::Result<()> {
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let histories = read("inputs/day9.txt", parser())?;
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let mut sum = 0;
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for mut h in histories {
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h.extend();
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sum += h.0.last().unwrap();
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}
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println!("{sum}");
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Ok(())
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}
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