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use std::{num::ParseIntError, str::FromStr};
use crate::{Problem, Solution};
pub struct Day09;
impl Problem for Day09 {
const DAY: u8 = 9;
const INPUT: &'static str = include_str!("../input/day_09.txt");
}
impl Solution for Day09 {
type Answer1 = usize;
type Answer2 = usize;
fn part_1(input: &str) -> anyhow::Result<Self::Answer1> {
let data = parse_input(input)?;
Ok(data.into_iter().map(extrapolate_forward).sum::<isize>() as usize)
}
fn part_2(input: &str) -> anyhow::Result<Self::Answer2> {
let data = parse_input(input)?;
Ok(data.into_iter().map(extrapolate_reverse).sum::<isize>() as usize)
}
}
fn parse_input(input: &str) -> Result<Vec<Vec<isize>>, ParseIntError> {
input.trim().lines().map(parse_line).collect()
}
fn parse_line(line: &str) -> Result<Vec<isize>, ParseIntError> {
line.split_whitespace().map(FromStr::from_str).collect()
}
fn extrapolate_forward(mut values: Vec<isize>) -> isize {
let mut value = 0;
while values.iter().any(|n| *n != 0) {
value += values.last().copied().unwrap();
values = values.array_windows().map(|[n, m]| m - n).collect();
}
value
}
fn extrapolate_reverse(mut values: Vec<isize>) -> isize {
let mut tails = Vec::new();
while values.iter().any(|n| *n != 0) {
tails.push(values.first().copied().unwrap());
values = values.array_windows().map(|[n, m]| m - n).collect();
}
tails.into_iter().rev().fold(0, |acc, n| n - acc)
}
#[cfg(test)]
mod tests {
use super::*;
const INPUT: &str = indoc::indoc! {"
0 3 6 9 12 15
1 3 6 10 15 21
10 13 16 21 30 45
"};
#[test]
fn test_part_1() -> anyhow::Result<()> {
Ok(assert_eq!(114, Day09::part_1(INPUT)?))
}
#[test]
fn test_part_2() -> anyhow::Result<()> {
Ok(assert_eq!(2, Day09::part_2(INPUT)?))
}
}
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