Day 3 solutions

Dependencies

• [2] B527MN66 Solve day 1 for 2020

Change contents

• file addition: day3.rs (----------)
  [2.17]
  + use std::env;

  + use std::io::BufRead;

  +

  + #[derive(Debug,Copy,Clone)]

  + enum Tile {

  + Blank,

  + Tree,

  + }

  +

  + struct Pairs<I> {

  + inner: I,

  + }

  +

  + impl<I> Pairs<I> {

  + fn new(inner: I) -> Self {

  + Pairs { inner: inner, }

  + }

  + }

  +

  + impl<I> Iterator for Pairs<I>

  + where I: Iterator {

  + type Item = (<I as Iterator>::Item, <I as Iterator>::Item);

  + fn next(&mut self) -> Option<Self::Item> {

  + let a = self.inner.next()?;

  + let b = self.inner.next()?;

  + Some((a,b))

  + }

  + }

  +

  + fn tile(c: char) -> Tile {

  + match c {

  + '.' => Tile::Blank,

  + '#' => Tile::Tree,

  + _ => panic!("Unrecognized tile")

  + }

  + }

  +

  + fn trees_hit(grid: &Vec<Vec<Tile>>, dx: usize, dy: usize) -> u64 {

  + let mut count = 0;

  + let mut x = 0;

  + for row in grid.iter().step_by(dy) {

  + match row[x % row.len()] {

  + Tile::Blank => {},

  + Tile::Tree => {count += 1;},

  + };

  + x += dx;

  + }

  + count

  + }

  +

  + fn main() {

  + let args: Vec<_> = env::args().collect();

  + let grid: Vec<Vec<Tile>> = std::io::BufReader::new(std::fs::File::open(&args[1]).unwrap())

  + .lines()

  + .map(Result::unwrap)

  + .map(|l| l

  + .chars()

  + .map(tile)

  + .collect()

  + )

  + .collect();

  + let slopes: Vec<(usize,usize)> = Pairs::new(args[2]

  + .split(",")

  + .map(|s| s.parse::<usize>().unwrap())

  + ).collect();

  +

  + println!("{}", slopes.iter()

  + .map(|(dx,dy)| trees_hit(&grid, *dx, *dy))

  + .product::<u64>()

  + );

  + }