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|
use nom::{
bytes::complete::tag,
character::complete::{i64, line_ending},
combinator::map,
multi::separated_list1,
sequence::tuple,
IResult,
};
use std::{collections::BTreeSet, fs, ops::Range};
fn main() -> Result<(), Box<dyn std::error::Error>> {
let input = fs::read_to_string("inputs/day_15.txt")?;
let sensors = Sensors::parser(&input).unwrap().1;
dbg!(sensors.count_covered_non_beacons_in_row(2000000));
dbg!(sensors
.find_hole_in_range(
Point { x: 0, y: 0 }..Point {
x: 4000001,
y: 4000001
}
)
.tuning_frequency());
Ok(())
}
#[derive(Debug, Clone)]
struct Sensors(Vec<Sensor>);
#[derive(Debug, Clone)]
struct Sensor {
center: Point,
closest_beacon: Point,
}
#[derive(Debug, Clone, PartialEq, Eq, PartialOrd, Ord)]
struct Point {
x: i64,
y: i64,
}
impl Sensors {
fn parser(input: &str) -> IResult<&str, Self> {
map(separated_list1(line_ending, Sensor::parser), Sensors)(input)
}
fn ranges_in_row(&self, y: i64) -> Vec<Range<i64>> {
let mut ranges: Vec<Range<i64>> = self
.0
.iter()
.filter_map(|s| s.get_range_in_row(y))
.collect();
let mut any_changes = true;
while any_changes {
any_changes = false;
ranges.sort_unstable_by_key(|r| r.start);
if ranges.len() > 0 {
for i in 0..ranges.len() - 1 {
if ranges[i].end > ranges[i + 1].start {
ranges[i + 1].start = ranges[i].end;
any_changes = true;
}
}
ranges.retain(|r| !r.is_empty());
}
}
ranges
}
fn count_covered_non_beacons_in_row(&self, y: i64) -> u64 {
let ranges = self.ranges_in_row(y);
// these beacons are all distinct, and are all definitely on
// the line because the beacons are how the line is found!
let beacons: BTreeSet<i64> = self
.0
.iter()
.filter(|s| s.closest_beacon.y == y)
.map(|s| s.closest_beacon.x)
.collect();
ranges.into_iter().map(|r| r.count() as u64).sum::<u64>() - beacons.len() as u64
}
fn find_hole_in_range(&self, field_range: Range<Point>) -> Point {
let full_row_len = field_range.end.x - field_range.start.x;
for y in field_range.start.y..field_range.end.y {
let ranges = self.ranges_in_row(y);
let count = ranges
.into_iter()
.map(|mut r| {
if r.start < field_range.start.x {
r.start = field_range.start.x
};
if r.end > field_range.end.x {
r.end = field_range.end.x
};
r
})
.map(|r| r.count() as i64)
.sum::<i64>();
if full_row_len != count {
for x in field_range.start.x..field_range.end.x {
let p = Point { x, y };
if !self.0.iter().any(|s| s.contains(&p)) {
return p;
}
}
}
}
panic!("Didn't find the hole as specified!")
}
}
impl Sensor {
fn parser(input: &str) -> IResult<&str, Self> {
map(
tuple((
tag("Sensor at "),
Point::parser,
tag(": closest beacon is at "),
Point::parser,
)),
|(_, center, _, closest_beacon)| Sensor {
center,
closest_beacon,
},
)(input)
}
fn get_range_in_row(&self, y: i64) -> Option<Range<i64>> {
let dy = (self.center.y - y).abs();
let dx = self.radius() - dy;
if dx < 0 {
None
} else {
let min_x = self.center.x - dx;
let max_x = self.center.x + dx;
Some(min_x..(max_x + 1))
}
}
fn radius(&self) -> i64 {
(self.center.x - self.closest_beacon.x).abs()
+ (self.center.y - self.closest_beacon.y).abs()
}
fn contains(&self, other: &Point) -> bool {
let d = (self.center.x - other.x).abs() + (self.center.y - other.y).abs();
d <= self.radius()
}
}
impl Point {
fn parser(input: &str) -> IResult<&str, Self> {
map(tuple((tag("x="), i64, tag(", y="), i64)), |(_, x, _, y)| {
Point { x, y }
})(input)
}
fn tuning_frequency(&self) -> i64 {
self.x * 4000000 + self.y
}
}
|
