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use nom::{
character::complete::{line_ending, one_of},
combinator::{map, map_res},
multi::{many1, separated_list1},
IResult,
};
use std::{collections::BTreeMap, fs};
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_15.txt")?;
let risk_grid = parse_risk_grid(&input).unwrap().1;
let big_risk_grid = risk_grid.expand();
{
let mut searcher = Searcher::new(risk_grid);
while searcher.end_risk().is_none() {
searcher.explore_next();
}
dbg!(searcher.end_risk());
}
{
let mut big_searcher = Searcher::new(big_risk_grid);
while big_searcher.end_risk().is_none() {
big_searcher.explore_next();
}
dbg!(big_searcher.end_risk());
}
Ok(())
}
#[derive(Debug)]
struct Searcher {
grid: RiskGrid,
frontier: Vec<(Risk, Point)>,
explored: BTreeMap<Point, Risk>,
}
impl Searcher {
fn new(grid: RiskGrid) -> Searcher {
let start = grid.start();
let mut explored = BTreeMap::new();
explored.insert(start.clone(), Risk(0));
Searcher {
grid,
explored,
frontier: vec![(Risk(0), start)],
}
}
fn explore_next(&mut self) {
if let Some((next_risk, next_point)) = self.frontier.pop() {
for (neighbour_risk, neighbour_point) in self.grid.neighbours(&next_point) {
if !self.explored.contains_key(&neighbour_point) {
let total_risk = next_risk + neighbour_risk;
self.explored.insert(neighbour_point.clone(), total_risk);
self.frontier.push((total_risk, neighbour_point));
}
}
self.frontier.sort_unstable_by(|a, b| b.0.cmp(&a.0));
}
}
fn end_risk(&self) -> Option<Risk> {
self.explored.get(&self.grid.end()).cloned()
}
}
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
struct Point {
x: usize,
y: usize,
}
#[derive(Debug)]
struct RiskGrid {
map: Vec<Vec<Risk>>,
}
impl RiskGrid {
fn start(&self) -> Point {
Point { x: 0, y: 0 }
}
fn end(&self) -> Point {
let y = self.map.len() - 1;
let x = self.map[y].len() - 1;
Point { x, y }
}
fn risk_at_point(&self, p: &Point) -> Option<Risk> {
self.map.get(p.y).and_then(|row| row.get(p.x)).cloned()
}
fn neighbours(&self, p: &Point) -> Vec<(Risk, Point)> {
let mut neighbours = Vec::new();
if p.x > 0 {
let left = Point { x: p.x - 1, y: p.y };
if let Some(risk) = self.risk_at_point(&left) {
neighbours.push((risk, left));
}
}
if p.y > 0 {
let up = Point { x: p.x, y: p.y - 1 };
if let Some(risk) = self.risk_at_point(&up) {
neighbours.push((risk, up));
}
}
let right = Point { x: p.x + 1, y: p.y };
if let Some(risk) = self.risk_at_point(&right) {
neighbours.push((risk, right));
}
let down = Point { x: p.x, y: p.y + 1 };
if let Some(risk) = self.risk_at_point(&down) {
neighbours.push((risk, down));
}
neighbours
}
fn expand(&self) -> RiskGrid {
let mut new_map = Vec::new();
for y_repeat in 0..5 {
for original_row in &self.map {
let mut new_row = Vec::new();
for x_repeat in 0..5 {
let risk_modifier = y_repeat + x_repeat;
for original_risk in original_row {
let modified_risk = original_risk.grid_wrap_increment(risk_modifier);
new_row.push(modified_risk);
}
}
new_map.push(new_row);
}
}
RiskGrid { map: new_map }
}
}
#[derive(Debug, Clone, Copy, derive_more::Add, PartialEq, Eq, PartialOrd, Ord)]
struct Risk(u64);
impl Risk {
fn grid_wrap_increment(&self, increment_count: u64) -> Risk {
let new = (self.0 + increment_count) % 9;
if new == 0 {
Risk(9)
} else {
Risk(new)
}
}
}
fn parse_risk_grid(input: &str) -> IResult<&str, RiskGrid> {
map(separated_list1(line_ending, many1(parse_risk)), |risks| {
RiskGrid { map: risks }
})(input)
}
fn parse_risk(input: &str) -> IResult<&str, Risk> {
map_res(one_of("0123456789"), |digit| {
digit.to_string().parse().map(Risk)
})(input)
}
|
