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day18
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‎src/day18.rs

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use std::str::FromStr;
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#[allow(dead_code)]
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struct LightGrid {
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grid: [[bool; 10000]; 2],
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}
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impl FromStr for LightGrid {
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type Err = String;
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fn from_str(light_grid_str: &str) -> Result<Self, Self::Err> {
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let mut light_grid = [[false; 10000]; 2];
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let mut i = 0;
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for b in light_grid_str.as_bytes() {
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match b {
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b'.' => i += 1,
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b'#' => {
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light_grid[0][i] = true;
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i += 1;
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}
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_ => (),
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}
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}
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Ok(Self { grid: light_grid })
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}
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}
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#[allow(dead_code)]
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impl LightGrid {
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const ROWS: usize = 100;
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#[inline(always)]
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fn get(&self, toggle: usize, i: usize, j: usize) -> bool {
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self.grid[toggle][i * Self::ROWS + j]
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}
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#[inline(always)]
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fn set(&mut self, toggle: usize, i: usize, j: usize, state: bool) {
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self.grid[toggle][i * Self::ROWS + j] = state;
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}
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fn get_neighbours(&self, i: usize, j: usize) -> impl Iterator<Item = (usize, usize)> {
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let neighbours: [(usize, usize); 8] = [
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(i.wrapping_sub(1), j.wrapping_sub(1)),
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(i.wrapping_sub(1), j),
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(i.wrapping_sub(1), j.wrapping_add(1)),
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(i, j.wrapping_sub(1)),
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(i, j.wrapping_add(1)),
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(i.wrapping_add(1), j.wrapping_sub(1)),
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(i.wrapping_add(1), j),
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(i.wrapping_add(1), j.wrapping_add(1)),
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];
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neighbours
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.into_iter()
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.filter(|pos| pos.0 < Self::ROWS && pos.1 < Self::ROWS)
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}
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fn step_100(&mut self) -> i32 {
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for step in 0..100 {
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for i in 0..Self::ROWS {
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for j in 0..Self::ROWS {
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let current_grid = step % 2;
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let next_grid = (step + 1) % 2;
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// Count ON neighbouring lights
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let count: i32 = self
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.get_neighbours(i, j)
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.map(|light| self.get(current_grid, light.0, light.1) as i32)
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.sum();
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// Apply rules
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if self.get(current_grid, i, j) {
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if count == 2 || count == 3 {
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self.set(next_grid, i, j, true);
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} else {
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self.set(next_grid, i, j, false);
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}
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} else if count == 3 {
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self.set(next_grid, i, j, true);
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} else {
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self.set(next_grid, i, j, false);
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}
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}
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}
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}
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self.grid[0].map(|light| light as i32).into_iter().sum()
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}
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const CORNERS: [(usize, usize); 4] = [(0, 0), (0, 99), (99, 0), (99, 99)];
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fn step_100_corners_always_on(&mut self) -> i32 {
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for step in 0..100 {
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for i in 0..Self::ROWS {
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for j in 0..Self::ROWS {
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// Skip corner
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if Self::CORNERS.contains(&(i, j)) {
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continue;
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}
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let current_grid = step % 2;
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let next_grid = (step + 1) % 2;
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// Count ON neighbouring lights
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let count: i32 = self
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.get_neighbours(i, j)
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.map(|light| self.get(current_grid, light.0, light.1) as i32)
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.sum();
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// Apply rules
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if self.get(current_grid, i, j) {
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if count == 2 || count == 3 {
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self.set(next_grid, i, j, true);
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} else {
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self.set(next_grid, i, j, false);
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}
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} else if count == 3 {
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self.set(next_grid, i, j, true);
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} else {
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self.set(next_grid, i, j, false);
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}
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}
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}
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}
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self.grid[0].map(|light| light as i32).into_iter().sum()
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}
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}
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#[cfg(test)]
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mod solution {
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use super::*;
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use crate::input::get_input::get_input;
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#[test]
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fn game_of_life() {
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let light_grid = get_input("light_grid").unwrap();
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let mut light_grid = light_grid.parse::<LightGrid>().unwrap();
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assert_eq!(light_grid.step_100(), 1061);
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}
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#[test]
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fn game_of_life_corners_always_on() {
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let light_grid = get_input("light_grid").unwrap();
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let mut light_grid = light_grid.parse::<LightGrid>().unwrap();
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for grid in 0..2 {
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light_grid.set(grid, 0, 0, true);
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light_grid.set(grid, 0, 99, true);
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light_grid.set(grid, 99, 0, true);
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light_grid.set(grid, 99, 99, true);
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}
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assert_eq!(light_grid.step_100_corners_always_on(), 1006);
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}
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}

‎src/input/light_grid.txt

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‎src/lib.rs

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Original file line numberDiff line numberDiff line change
@@ -10,6 +10,7 @@ mod day14;
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mod day15;
1111
mod day16;
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mod day17;
13+
mod day18;
1314
mod day2;
1415
mod day3;
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mod day4;

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