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use advent_of_code::prelude::*;
#[derive(Debug, Clone, Eq, PartialEq, Hash)]
pub enum Cell {
Down,
Right,
None,
}
impl Default for Cell {
fn default() -> Self {
Self::None
}
}
#[derive(Debug, Clone, Eq, PartialEq)]
pub struct Map {
grid: Grid<Cell>,
}
impl Map {
fn step(&self) -> Self {
self.step_east().step_south()
}
fn step_east(&self) -> Self {
let mut step = self.clone();
for ((Row(row), Col(col)), cell) in self.grid.indexed_cells() {
if *cell == Cell::Right {
let mut next = col + 1;
if next >= self.grid.cols().0 {
next = 0;
}
if self.grid[Row(row)][Col(next)] == Cell::None {
step.grid[Row(row)][Col(next)] = Cell::Right;
step.grid[Row(row)][Col(col)] = Cell::None;
}
}
}
step
}
fn step_south(&self) -> Self {
let mut step = self.clone();
for ((Row(row), Col(col)), cell) in self.grid.indexed_cells() {
if *cell == Cell::Down {
let mut next = row + 1;
if next >= self.grid.rows().0 {
next = 0;
}
if self.grid[Row(next)][Col(col)] == Cell::None {
step.grid[Row(next)][Col(col)] = Cell::Down;
step.grid[Row(row)][Col(col)] = Cell::None;
}
}
}
step
}
}
pub fn parse(fh: File) -> Result<Map> {
Ok(Map {
grid: parse::grid(parse::raw_lines(fh), |b, _, _| match b {
b'v' => Cell::Down,
b'>' => Cell::Right,
b'.' => Cell::None,
_ => panic!("unknown cell {}", b),
}),
})
}
pub fn part1(map: Map) -> Result<u64> {
let mut prev = map;
let mut i = 0;
loop {
i += 1;
let next = prev.step();
if next == prev {
break;
}
prev = next;
}
Ok(i)
}
pub fn part2(_: Map) -> Result<i64> {
Ok(0)
}
#[test]
fn test() {
assert_eq!(
part1(parse(parse::data(2021, 25).unwrap()).unwrap()).unwrap(),
482
);
}
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