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|
use nom::{
character::complete::{i32 as nom_i32, line_ending, space1},
combinator::map,
multi::separated_list1,
IResult,
};
use std::fs;
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_9.txt")?;
let parsed = DataSequences::parser(&input).unwrap().1;
dbg!(&parsed.sum_extrapolated_values());
dbg!(&parsed.sum_extrapolated_front_values());
Ok(())
}
#[derive(Debug)]
struct DataSequences(Vec<DataSequence>);
#[derive(Debug)]
struct DataSequence(Vec<i32>);
impl DataSequences {
fn parser(input: &str) -> IResult<&str, Self> {
map(
separated_list1(line_ending, DataSequence::parser),
DataSequences,
)(input)
}
fn sum_extrapolated_values(&self) -> i32 {
self.0.iter().map(|d| d.extrapolate()).sum()
}
fn sum_extrapolated_front_values(&self) -> i32 {
self.0.iter().map(|d| d.extrapolate_front()).sum()
}
}
impl DataSequence {
fn parser(input: &str) -> IResult<&str, Self> {
map(separated_list1(space1, nom_i32), DataSequence)(input)
}
fn extrapolate(&self) -> i32 {
let mut differential_tree = vec![self.0.clone()];
while !differential_tree
.last()
.map_or(true, |l| l.iter().all(|i| *i == 0))
{
let last_row = differential_tree.last().unwrap();
let mut new_row = Vec::with_capacity(last_row.len() - 1);
for i in 0..last_row.len() - 1 {
new_row.push(last_row[i + 1] - last_row[i]);
}
differential_tree.push(new_row);
}
differential_tree.last_mut().unwrap().push(0);
while differential_tree.len() > 1 {
let bottom_row = differential_tree.pop().unwrap();
let new_last = differential_tree.last_mut().unwrap();
new_last.push(new_last.last().unwrap() + bottom_row.last().unwrap());
}
differential_tree
.last()
.and_then(|l| l.last())
.copied()
.unwrap()
}
fn extrapolate_front(&self) -> i32 {
let backwards = DataSequence(self.0.iter().rev().copied().collect());
backwards.extrapolate()
}
}
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