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use std::io::{self, Read};
#[derive(Clone, Copy, PartialEq, Eq)]
enum Tile {
Safe,
Trap,
}
impl From<char> for Tile {
fn from(ch: char) -> Tile {
match ch {
'.' => Tile::Safe,
'^' => Tile::Trap,
_ => panic!("invalid tile char {}", ch),
}
}
}
struct Map {
rows: Vec<Box<[Tile]>>,
}
impl Map {
fn generate_row(&mut self) {
let mut next = Vec::new();
{
let previous = self.rows.last().unwrap();
for (i, ¢er) in self.rows.last().unwrap().iter().enumerate() {
let left = previous.get(i.wrapping_sub(1)).cloned().unwrap_or(Tile::Safe);
let right = previous.get(i + 1).cloned().unwrap_or(Tile::Safe);
let tile = match (left, center, right) {
(Tile::Trap, Tile::Trap, Tile::Safe) => Tile::Trap,
(Tile::Safe, Tile::Trap, Tile::Trap) => Tile::Trap,
(Tile::Trap, Tile::Safe, Tile::Safe) => Tile::Trap,
(Tile::Safe, Tile::Safe, Tile::Trap) => Tile::Trap,
_ => Tile::Safe,
};
next.push(tile);
}
}
self.rows.push(next.into_boxed_slice());
}
fn count_safe(&self) -> usize {
self.rows.iter()
.map(|row| {
row.iter()
.filter(|&&t| t == Tile::Safe)
.count()
})
.sum()
}
}
impl<'a> From<&'a str> for Map {
fn from(s: &'a str) -> Map {
let rows = s.lines()
.map(|l| l.chars().map(Tile::from).collect::<Vec<_>>().into_boxed_slice())
.collect();
Map { rows: rows }
}
}
fn solve(rows: u32, input: &str) -> usize {
let mut map = Map::from(input);
for _ in 1..rows {
map.generate_row();
}
map.count_safe()
}
fn main() {
let mut input = String::new();
io::stdin().read_to_string(&mut input).unwrap();
println!("Part 1: {}", solve(40, &input));
println!("Part 2: {}", solve(400000, &input));
}
#[test]
fn part1() {
assert_eq!(6, solve(3, "..^^."));
assert_eq!(38, solve(10, ".^^.^.^^^^"));
}
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