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use {
anyhow::{
anyhow,
Context,
Result,
},
std::{
env::args,
fs::File,
io::{
BufRead,
BufReader,
},
path::Path,
},
};
fn read_input<T: AsRef<Path>>(filename: T) -> Result<Vec<usize>> {
let reader = BufReader::new(File::open(filename)?);
reader.lines().map(
|v| v?.parse().map_err(|err| anyhow!("Could not parse input: {}", err))
).collect()
}
#[derive(PartialEq)]
enum Change {
NoPrevVal,
Increased,
Decreased,
Identical,
}
fn count_increases<'a, I: IntoIterator<Item = &'a usize>>(values: I) -> usize {
let changes: Vec<Change> = values.into_iter().scan(None, |state, val| {
let next = match state {
None => Change::NoPrevVal,
Some(prev) if val < *prev => Change::Decreased,
Some(prev) if val > *prev => Change::Increased,
Some(prev) if val == *prev => Change::Identical,
Some(_) => unreachable!(),
};
*state = Some(val);
Some(next)
}).collect();
changes.iter().fold(0, |count, change|
if *change == Change::Increased { count + 1 } else { count }
)
}
fn part1<'a, I: IntoIterator<Item = &'a usize>>(input: I) -> Result<usize> {
let count = count_increases(input);
Ok(count)
}
fn part2<'a, I: IntoIterator<Item = &'a usize> + Copy>(input: I) -> Result<usize> {
let left_iter = input.into_iter();
let middle_iter = input.into_iter().skip(1);
let right_iter = input.into_iter().skip(2);
let slidesums: Vec<_> = left_iter.zip(middle_iter).zip(right_iter).map(|n| {
let ((first, second), third) = n;
first + second + third
}).collect();
let count = count_increases(&slidesums);
Ok(count)
}
fn main() -> Result<()> {
let ( do_part_1, do_part_2 ) = aoc::do_parts();
let filename = args().nth(1).ok_or(anyhow!("Missing input filename"))?;
let input = read_input(filename).context("Could not read input")?;
if do_part_1 {
let solution = part1(&input).context("No solution for part 1")?;
println!("Part1, number of increases found to be: {}", solution);
}
if do_part_2 {
let solution = part2(&input).context("No solution for part 2")?;
println!("Part2, number of increases found to be: {}", solution);
}
Ok(())
}
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