Created
December 24, 2019 19:04
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| use std::fs::File; | |
| use std::io::{BufRead, BufReader, Result}; | |
| use std::collections::HashSet; | |
| type Grid = (i32, isize, isize); | |
| fn load_grid(path: &str) -> Result<Grid> { | |
| let f = File::open(path)?; | |
| let f = BufReader::new(f); | |
| let (mut grid, mut rows, mut cols) = (0, 0, 0); | |
| for (r, line) in f.lines().enumerate() { | |
| let line = line.unwrap(); | |
| cols = line.len(); | |
| rows = rows.max(r + 1); | |
| for (c, cell) in line.chars().enumerate() { | |
| if cell == '#' { | |
| let pos = (r * cols + c); | |
| grid = grid | (1 << pos); | |
| } | |
| } | |
| } | |
| Ok((grid, rows as isize, cols as isize)) | |
| } | |
| const DIRS: [(isize, isize); 4] = [(-1, 0), (1, 0), (0, 1), (0, -1)]; | |
| fn solve() { | |
| let (mut current, rows, cols) = load_grid("input-day24.txt").unwrap(); | |
| println!("{} {} {}", current, rows, cols); | |
| let mut seen: HashSet<i32> = HashSet::new(); | |
| loop { | |
| let mut next = 0i32; | |
| for r in 0..rows { | |
| for c in 0..cols { | |
| let mut adjacent = 0; | |
| for (dr, dc) in &DIRS { | |
| let (ar, ac) = (r + dr, c + dc); | |
| if ar >= 0 && ar < rows && ac >= 0 && ac < cols { | |
| adjacent += (current >> (ar * cols + ac) & 1); | |
| } | |
| } | |
| let next_cell = match (current >> (r * cols + c) & 1) { | |
| 1 if adjacent != 1 => 0, | |
| 0 if adjacent == 1 || adjacent == 2 => 1, | |
| x => x, | |
| }; | |
| next = next | (next_cell << (r * cols + c)); | |
| } | |
| } | |
| current = next; | |
| if seen.contains(¤t) { | |
| break; | |
| } | |
| seen.insert(current); | |
| } | |
| println!("{}", current); | |
| } |
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