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use anyhow::{Result, anyhow};
use std::env::args;
use std::fs::File;
use std::io::{BufRead, BufReader};
use std::ops::AddAssign;
use std::path::Path;
use thiserror::Error;
#[derive(Clone,Copy)]
struct CoordPair {
x: usize,
y: usize,
}
impl AddAssign for CoordPair {
fn add_assign(&mut self, other: Self) {
*self = Self {
x: self.x + other.x,
y: self.y + other.y,
};
}
}
#[derive(Debug)]
struct TreeMap {
width: usize,
height: usize,
map: Vec<bool>,
}
#[derive(Error, Debug)]
pub enum TreeError {
#[error("Could not access TreeMap")]
Invalid,
}
impl TreeMap {
fn is_tree(&self, pos: CoordPair) -> Result<bool, TreeError> {
let mut p = pos;
p.x %= self.width;
self.map.get(p.y * self.width + p.x).copied().ok_or(TreeError::Invalid)
}
}
fn read_input<T: AsRef<Path>>(filename: T) -> Result<TreeMap> {
let f = File::open(filename)?;
let reader = BufReader::new(f);
let tree_map = reader.lines()
.fold(Ok(TreeMap { width: 0, height: 0, map: vec![] }), |acc, l| {
let line = l?;
let row: Result<Vec<bool>> = line.chars().map(|c| match c {
'#' => Ok(true),
'.' => Ok(false),
_ => Err(anyhow!("Invalid map character: '{}'", c)),
}).collect();
match acc {
Ok(mut a) => {
a.map.append(&mut row?);
a.height += 1;
Ok(a)
},
Err(err) => Err(err)
}
});
match tree_map {
Ok(mut tm) => {
tm.width = tm.map.len()/tm.height;
Ok(tm)
},
err => err,
}
}
fn part1(input: &TreeMap) -> Result<usize> {
let mut pos = CoordPair { x: 0, y: 0, };
let slope = CoordPair { x: 3, y: 1, };
let mut collision_count = 0;
while pos.y < input.height {
if input.is_tree(pos)? {
collision_count += 1;
}
pos += slope;
}
Ok(collision_count)
}
fn part2(input: &TreeMap) -> Result<usize> {
let slopes = vec![
CoordPair { x: 1, y: 1, },
CoordPair { x: 3, y: 1, },
CoordPair { x: 5, y: 1, },
CoordPair { x: 7, y: 1, },
CoordPair { x: 1, y: 2, },
];
let res = slopes.iter().map(|slope| {
let mut pos = CoordPair { x: 0, y: 0, };
let mut collision_count = 0;
while pos.y < input.height {
if input.is_tree(pos)? {
collision_count += 1;
}
pos += *slope;
}
Ok(collision_count)
}).product();
res
}
fn main() {
let ( do_part_1, do_part_2 ) = aoc::do_parts();
let filename = match args().nth(1) {
Some(f) => f,
None => {
eprintln!("Missing input filename");
std::process::exit(1);
},
};
match read_input(filename) {
Ok(input) => {
if do_part_1 {
match part1(&input) {
Ok(solution) => println!("Part1: would encounter {} trees", solution),
Err(err) => {
eprintln!("Part1, no solution found: {}", err);
std::process::exit(1);
}
};
}
if do_part_2 {
match part2(&input) {
Ok(solution) => println!("Part2: {} is the product of all tree collisions", solution),
Err(err) => {
eprintln!("Part2, no solution found: {}", err);
std::process::exit(1);
}
};
}
},
Err(err) => eprintln!("Could not read input: {}", err),
}
}
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