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use nom::{
branch::alt,
character::complete::{char as nom_char, line_ending},
combinator::{map, value},
multi::{many1, separated_list1},
IResult,
};
use std::fs;
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_25.txt")?;
let mut seafloor = parse_seafloor(&input).unwrap().1;
for i in 1.. {
let next = seafloor.next();
if next == seafloor {
dbg!(i);
break;
}
seafloor = next;
}
Ok(())
}
#[derive(Debug, PartialEq, Eq)]
struct Seafloor(Vec<Vec<Option<Cucumber>>>);
impl Seafloor {
fn next(&self) -> Seafloor {
self.next_east().next_south()
}
fn next_east(&self) -> Seafloor {
let mut results = Vec::new();
for y in 0..self.0.len() {
let mut current_row = Vec::new();
for x in 0..self.0[y].len() {
let old = &self.0[y][x];
let old_left = &self.0[y][if x == 0 { self.0[y].len() - 1 } else { x - 1 }];
let old_right = &self.0[y][(x + 1) % self.0[y].len()];
let new = if *old == None && *old_left == Some(Cucumber::East) {
old_left.clone()
} else if *old == Some(Cucumber::East) && *old_right == None {
None
} else {
old.clone()
};
current_row.push(new);
}
results.push(current_row);
}
Seafloor(results)
}
fn next_south(&self) -> Seafloor {
let mut results = Vec::new();
for y in 0..self.0.len() {
let mut current_row = Vec::new();
for x in 0..self.0[y].len() {
let old = &self.0[y][x];
let old_up = &self.0[if y == 0 { self.0.len() - 1 } else { y - 1 }][x];
let old_down = &self.0[(y + 1) % self.0.len()][x];
let new = if *old == None && *old_up == Some(Cucumber::South) {
old_up.clone()
} else if *old == Some(Cucumber::South) && *old_down == None {
None
} else {
old.clone()
};
current_row.push(new);
}
results.push(current_row);
}
Seafloor(results)
}
}
#[derive(Debug, Clone, PartialEq, Eq)]
enum Cucumber {
East,
South,
}
fn parse_seafloor(input: &str) -> IResult<&str, Seafloor> {
map(
separated_list1(line_ending, many1(parse_cucumber)),
Seafloor,
)(input)
}
fn parse_cucumber(input: &str) -> IResult<&str, Option<Cucumber>> {
alt((
value(None, nom_char('.')),
value(Some(Cucumber::East), nom_char('>')),
value(Some(Cucumber::South), nom_char('v')),
))(input)
}
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