2020: day11: part 2
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@ -1,5 +1,4 @@
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use std::fmt::Write;
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use std::fmt::Write;
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use std::mem;
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use aoc::err;
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use aoc::err;
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@ -9,6 +8,7 @@ pub fn run() -> aoc::Result<String> {
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let mut res = String::with_capacity(128);
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let mut res = String::with_capacity(128);
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writeln!(res, "part 1: {}", part1(INPUT)?)?;
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writeln!(res, "part 1: {}", part1(INPUT)?)?;
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writeln!(res, "part 2: {}", part2(INPUT)?)?;
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Ok(res)
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Ok(res)
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}
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}
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@ -16,7 +16,17 @@ pub fn run() -> aoc::Result<String> {
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fn part1(input: &str) -> aoc::Result<usize> {
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fn part1(input: &str) -> aoc::Result<usize> {
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let mut layout: Layout = input.parse()?;
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let mut layout: Layout = input.parse()?;
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layout.converge();
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let occupied_threshold = 4;
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layout.converge(occupied_threshold, Layout::count_adjacent);
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Ok(layout.occupied_seats())
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}
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fn part2(input: &str) -> aoc::Result<usize> {
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let mut layout: Layout = input.parse()?;
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let occupied_threshold = 5;
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layout.converge(occupied_threshold, Layout::count_line_of_sight);
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Ok(layout.occupied_seats())
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Ok(layout.occupied_seats())
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}
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}
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@ -38,10 +48,15 @@ struct Layout {
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impl Layout {
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impl Layout {
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/// Steps one round in the simulation, returns the previous grid
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/// Steps one round in the simulation, returns the previous grid
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fn step(&mut self) -> Grid {
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fn step(
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&mut self,
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occupied_threshold: u8,
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adj_count: fn(&Self, usize, usize, Cell) -> u8,
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) -> bool {
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let grid = &self.grid;
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let grid = &self.grid;
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let mut new = grid.clone();
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let mut new = grid.clone();
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let mut changed = false;
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for i in 0..self.height {
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for i in 0..self.height {
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for j in 0..self.width {
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for j in 0..self.width {
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@ -49,13 +64,15 @@ impl Layout {
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match cell {
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match cell {
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Cell::EmptySeat => {
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Cell::EmptySeat => {
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if self.count_adjacent(i, j, Cell::OccupiedSeat) == 0 {
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if adj_count(&self, i, j, Cell::OccupiedSeat) == 0 {
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new[i][j] = Cell::OccupiedSeat;
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new[i][j] = Cell::OccupiedSeat;
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changed = true;
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}
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}
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}
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}
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Cell::OccupiedSeat => {
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Cell::OccupiedSeat => {
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if self.count_adjacent(i, j, Cell::OccupiedSeat) >= 4 {
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if adj_count(&self, i, j, Cell::OccupiedSeat) >= occupied_threshold {
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new[i][j] = Cell::EmptySeat;
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new[i][j] = Cell::EmptySeat;
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changed = true;
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}
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}
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}
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}
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_ => {}
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_ => {}
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@ -63,16 +80,14 @@ impl Layout {
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}
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}
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}
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}
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mem::replace(&mut self.grid, new)
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self.grid = new;
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changed
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}
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}
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/// Steps through the simulation until a fixpoint is reached
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/// Steps through the simulation until a fixpoint is reached
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fn converge(&mut self) {
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fn converge(&mut self, occupied_threshold: u8, adj_count: fn(&Self, usize, usize, Cell) -> u8) {
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let mut prev = self.step();
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while self.step(occupied_threshold, adj_count) {}
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while prev != self.grid {
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prev = self.step();
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}
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}
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}
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const OFFSETS: &'static [(i8, i8)] = &[
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const OFFSETS: &'static [(i8, i8)] = &[
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@ -105,6 +120,36 @@ impl Layout {
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count
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count
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}
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}
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fn count_line_of_sight(&self, i: usize, j: usize, value: Cell) -> u8 {
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let mut count = 0;
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for (di, dj) in Self::OFFSETS {
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let mut distance = 1;
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let diff = loop {
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let (di, dj) = (di * distance, dj * distance);
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let (i, j) = (i.wrapping_add(di as usize), j.wrapping_add(dj as usize));
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let cell = self.grid.get(i).map(|line| line.get(j)).flatten();
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match cell {
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// keep going, the next seat is farther away
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Some(Cell::Floor) => distance += 1,
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// found the kind of seat we care about
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Some(&seat) if seat == value => break 1,
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// found a seat that blocks line of sight, or reached out of bounds
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Some(_) | None => break 0,
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}
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};
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// only check seat if it's in bounds
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count += diff;
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}
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count
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}
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fn occupied_seats(&self) -> usize {
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fn occupied_seats(&self) -> usize {
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self.grid
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self.grid
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.iter()
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.iter()
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@ -175,4 +220,14 @@ mod tests {
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fn part1_real() {
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fn part1_real() {
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assert_eq!(part1(INPUT).unwrap(), 2427);
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assert_eq!(part1(INPUT).unwrap(), 2427);
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}
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}
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#[test]
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fn part2_provided() {
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assert_eq!(part2(PROVIDED).unwrap(), 26);
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}
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#[test]
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fn part2_real() {
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assert_eq!(part2(INPUT).unwrap(), 2199);
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}
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}
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}
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