64 lines
1.6 KiB
Rust
64 lines
1.6 KiB
Rust
#![warn(clippy::all, clippy::pedantic)]
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use nom::{character::complete, multi::separated_list1, IResult};
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use std::{iter::successors, ops::Not};
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/// day 9 part 2 of aoc 2023
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///
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/// # Arguments
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/// - input the input for today's puzzle
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///
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/// # Panics
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/// panics whne it cannot parse the input OR when ever the number of game numbers is greater than
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/// usize
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#[must_use]
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pub fn part2(input: &str) -> String {
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let (_, report) = parse_input(input).expect("should have valid input for aoc");
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report.iter().map(|x| get_next(x)).sum::<i64>().to_string()
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}
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fn get_next(array: &[i64]) -> i64 {
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let array = Vec::from(array);
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let mut a = successors(Some(array.clone()), |a| {
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a.iter()
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.all(|x| x == &0)
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.not()
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.then_some(a.windows(2).map(|a| a[1] - a[0]).collect::<Vec<_>>())
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})
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.map(|x| *x.first().unwrap())
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.collect::<Vec<_>>();
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a.reverse();
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a.iter().fold(0, |acc, x| x - acc)
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}
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fn parse_input(input: &str) -> IResult<&str, Vec<Vec<i64>>> {
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separated_list1(
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complete::line_ending,
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separated_list1(complete::space1, complete::i64),
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)(input)
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}
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#[cfg(test)]
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mod test {
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use super::*;
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use rstest::rstest;
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#[rstest]
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#[case(vec![0,3,6,9,12,15], -3)]
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#[case(vec![1,3,6,10,15,21], 0)]
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#[case(vec![10,13,16,21,30,45], 5)]
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fn part2_next(#[case] array: Vec<i64>, #[case] expected: i64) {
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assert_eq!(get_next(&array), expected);
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}
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const INPUT: &str = "0 3 6 9 12 15
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1 3 6 10 15 21
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10 13 16 21 30 45";
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#[test]
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fn part2_works() {
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let result = part2(INPUT);
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assert_eq!(result, "2".to_string());
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}
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}
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