Day 9 part 2
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Quentin Boyer
parent
cc2e040332
commit
3ba0a0b6c6
1 changed files with 267 additions and 3 deletions
270
src/bin/day9.rs
270
src/bin/day9.rs
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@ -1,8 +1,9 @@
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use std::time::Instant;
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use std::{collections::HashSet, ops::RangeInclusive, time::Instant};
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use aoc_2025::{load, print_res};
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use bstr::BString;
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#[derive(PartialEq, Eq, Hash, Debug, Clone, Copy)]
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pub struct Point2 {
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x: u64,
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y: u64,
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@ -26,22 +27,285 @@ pub fn parsing(input: &BString) -> color_eyre::Result<Parsed> {
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.collect()
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}
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fn rect_area(a: &Point2, b: &Point2) -> u64 {
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(a.x.abs_diff(b.x) + 1) * (a.y.abs_diff(b.y) + 1)
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}
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#[inline(never)]
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pub fn part1(input: Parsed) {
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let max_area = input
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.iter()
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.enumerate()
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.flat_map(|(ia, a)| input.iter().skip(ia + 1).map(move |b| (a, b)))
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.map(|(a, b)| (a.x.abs_diff(b.x) + 1) * (a.y.abs_diff(b.y) + 1))
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.map(|(a, b)| rect_area(a, b))
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.max()
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.unwrap();
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print_res!("Max area: {max_area}");
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}
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struct Polygon {
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points: Vec<Point2>,
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x_values: Vec<u64>,
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y_values: Vec<u64>,
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vertical_edges_by_x_slot: Vec<Vec<RangeInclusive<u64>>>,
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horizontal_edges_by_y_slot: Vec<Vec<RangeInclusive<u64>>>,
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}
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impl Polygon {
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pub fn new(points: Vec<Point2>) -> Self {
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let x_values = {
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let x: HashSet<_> = points.iter().map(|p| p.x).collect();
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let mut x: Vec<_> = x.into_iter().collect();
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x.sort_unstable();
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x
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};
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let y_values = {
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let y: HashSet<_> = points.iter().map(|p| p.y).collect();
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let mut y: Vec<_> = y.into_iter().collect();
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y.sort_unstable();
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y
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};
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let mut this = Polygon {
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points,
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vertical_edges_by_x_slot: vec![Vec::new(); x_values.len()],
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horizontal_edges_by_y_slot: vec![Vec::new(); y_values.len()],
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x_values,
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y_values,
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};
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for (i, p) in this.points.iter().enumerate() {
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let prev = this.prev(i);
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if prev.x == p.x {
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let x_stop = this.x_values.iter().position(|&x| x == p.x).unwrap();
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// Vertical edge
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let min_y = p.y.min(prev.y);
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let max_y = p.y.max(prev.y);
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this.vertical_edges_by_x_slot[x_stop].push(min_y..=max_y);
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} else {
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let y_stop = this.y_values.iter().position(|&y| y == p.y).unwrap();
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assert_eq!(prev.y, p.y);
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let min_x = p.x.min(prev.x);
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let max_x = p.x.max(prev.x);
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this.horizontal_edges_by_y_slot[y_stop].push(min_x..=max_x);
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}
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}
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this
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}
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pub fn contains(&self, point: Point2) -> bool {
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// Is the point a corner?
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if self.points.contains(&point) {
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return true;
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}
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// On a horizontal edge
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if let Some(y_stop) = self.y_values.iter().position(|&y| y == point.y) {
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let edges = &self.horizontal_edges_by_y_slot[y_stop];
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if edges.iter().any(|e| e.contains(&point.x)) {
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return true;
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}
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}
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// On a vertical edge
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if let Some(x_stop) = self.x_values.iter().position(|&x| x == point.x) {
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let edges = &self.vertical_edges_by_x_slot[x_stop];
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if edges.iter().any(|e| e.contains(&point.y)) {
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return true;
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}
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}
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// Not on the boundary
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let mut intersection_count = 0;
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// Check all vertical edges starting from this point
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for (slot, _x) in self
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.x_values
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.iter()
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.enumerate()
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.skip_while(|&(_, &x)| x < point.x)
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.take_while(|&(_, &x)| point.x <= x)
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{
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let edges = &self.vertical_edges_by_x_slot[slot];
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if let Some(edge) = edges.iter().find(|r| r.contains(&point.y)) {
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let intersect = if point.y == *edge.start() {
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*edge.end() > point.y
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} else if point.y == *edge.end() {
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*edge.start() > point.y
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} else {
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true
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};
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if intersect {
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intersection_count += 1;
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}
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}
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}
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intersection_count % 2 == 1
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}
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pub fn points(&self) -> &[Point2] {
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&self.points
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}
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pub fn x_values(&self) -> &[u64] {
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&self.x_values
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}
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pub fn y_values(&self) -> &[u64] {
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&self.y_values
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}
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pub fn prev(&self, index: usize) -> Point2 {
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if index == 0 {
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*self.points.last().unwrap()
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} else {
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self.points[index - 1]
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}
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}
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}
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fn horizontal_edges_contained(poly: &Polygon, a: Point2, b: Point2) -> bool {
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assert_ne!(a.x, b.x);
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let min_x = a.x.min(b.x);
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let max_x = a.x.max(b.x);
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let y_values: &[u64] = if a.y == b.y { &[a.y] } else { &[a.y, b.y] };
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for &y in y_values {
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// Left corner
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if !poly.contains(Point2 { x: min_x, y }) {
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return false;
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}
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if !poly.contains(Point2 { x: min_x + 1, y }) {
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return false;
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}
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// Inside edges
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for &x in poly
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.x_values()
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.iter()
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.skip_while(|&&x| x <= min_x)
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.take_while(|&&x| x < max_x)
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{
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if !poly.contains(Point2 { x, y })
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|| !poly.contains(Point2 { x: x - 1, y })
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|| !poly.contains(Point2 { x: x + 1, y })
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{
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return false;
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}
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}
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// Right corner
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if !poly.contains(Point2 { x: max_x, y }) {
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return false;
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}
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if !poly.contains(Point2 { x: max_x - 1, y }) {
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return false;
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}
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}
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true
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}
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fn vertical_edges_contain(poly: &Polygon, a: Point2, b: Point2) -> bool {
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assert_ne!(a.y, b.y);
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let min_y = a.y.min(b.y);
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let max_y = a.y.max(b.y);
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let x_values: &[u64] = if a.x == b.x { &[a.x] } else { &[a.x, b.x] };
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for &x in x_values {
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// Bottom corner
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if !poly.contains(Point2 { x, y: min_y }) {
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return false;
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}
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if !poly.contains(Point2 { x, y: min_y + 1 }) {
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return false;
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}
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// Inside edges
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for &y in poly
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.y_values()
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.iter()
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.skip_while(|&&y| y <= min_y)
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.take_while(|&&y| y < max_y)
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{
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if !poly.contains(Point2 { x, y })
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|| !poly.contains(Point2 { x, y: y - 1 })
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|| !poly.contains(Point2 { x, y: y + 1 })
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{
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return false;
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}
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}
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// Top corner
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if !poly.contains(Point2 { x, y: max_y }) {
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return false;
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}
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if !poly.contains(Point2 { x, y: max_y - 1 }) {
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return false;
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}
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}
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true
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}
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#[inline(never)]
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pub fn part2(input: Parsed) {
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todo!("todo part2")
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let poly = Polygon::new(input);
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let mut max_area = 0;
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for (ia, &a) in poly.points().iter().enumerate() {
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for &b in poly.points().iter().skip(ia + 1) {
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let area = rect_area(&a, &b);
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// Area would not even be bigger, don’t attempt to validate it
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if area < max_area {
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continue;
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}
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assert!(area > 1);
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if a.x != b.x && !horizontal_edges_contained(&poly, a, b) {
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continue;
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}
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if a.y != b.y && !vertical_edges_contain(&poly, a, b) {
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continue;
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}
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max_area = area;
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}
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}
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print_res!("Max inside area: {max_area}");
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}
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pub fn main() -> color_eyre::Result<()> {
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