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+extern crate regex;
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+
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+use std::collections::{HashMap, VecDeque};
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+use std::error::Error;
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+use std::fmt;
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+use std::fs;
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+use std::result;
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+use std::str::FromStr;
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+
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+use regex::Regex;
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+
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+type Result<T> = result::Result<T, Box<Error>>;
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+
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+const INPUT: &str = "inputs/12.txt";
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+
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+#[derive(Debug, PartialEq)]
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+struct Pots(VecDeque<bool>);
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+
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+#[derive(Debug, PartialEq)]
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+struct SpreadRules(HashMap<[bool; 5], bool>);
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+
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+#[derive(Debug, PartialEq)]
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+struct GrowthSimulation {
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+ pots: Pots,
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+ spread_rules: SpreadRules,
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+ generations: usize,
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+}
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+
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+impl fmt::Display for Pots {
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+ #[allow(clippy::write_with_newline)]
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+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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+ for pot in self.0.iter() {
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+ if *pot {
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+ write!(f, "#")?;
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+ } else {
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+ write!(f, ".")?;
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+ }
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+ }
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+ write!(f, "\n")?;
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+ Ok(())
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+ }
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+}
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+
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+impl fmt::Display for SpreadRules {
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+ #[allow(clippy::write_with_newline)]
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+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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+ for (pattern, result) in self.0.iter() {
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+ for pot in pattern {
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+ if *pot {
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+ write!(f, "#")?;
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+ } else {
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+ write!(f, ".")?;
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+ }
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+ }
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+ write!(f, " => ")?;
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+ if *result {
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+ write!(f, "#")?;
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+ } else {
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+ write!(f, ".")?;
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+ }
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+ write!(f, "\n")?;
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+ }
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+ write!(f, "\n")?;
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+ Ok(())
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+ }
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+}
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+
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+impl fmt::Display for GrowthSimulation {
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+ #[allow(clippy::write_with_newline)]
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+ fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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+ write!(f, "{}", self.pots)?;
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+ write!(f, "\n")?;
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+ write!(f, "{}", self.spread_rules)?;
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+ Ok(())
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+ }
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+}
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+
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+impl FromStr for GrowthSimulation {
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+ type Err = Box<Error>;
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+
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+ fn from_str(s: &str) -> Result<GrowthSimulation> {
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+ let sections: Vec<&str> = s.split("\n\n").collect();
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+ let (initial_state_str, spread_rules_str) = (sections[0], sections[1]);
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+ let mut pots = Pots(VecDeque::new());
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+ let mut spread_rules = SpreadRules(HashMap::new());
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+
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+ lazy_static! {
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+ static ref initial_state_regex: Regex =
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+ Regex::new(r"initial state: (?P<initial_state>[#.]+)").unwrap();
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+ static ref spread_rules_regex: Regex =
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+ Regex::new(r"(?P<pattern>[#.]{5}) => (?P<result>[#.])").unwrap();
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+ }
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+
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+ let initial_state_captures = match initial_state_regex.captures(initial_state_str) {
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+ None => {
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+ return Err(From::from(
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+ "Malformed initial state, no fields could be found",
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+ ));
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+ }
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+ Some(captures) => captures,
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+ };
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+
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+ for pot in initial_state_captures["initial_state"].chars() {
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+ pots.0.push_back(pot == '#');
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+ }
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+
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+ for rule in spread_rules_str.lines() {
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+ let spread_rules_captures = match spread_rules_regex.captures(rule) {
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+ None => {
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+ return Err(From::from(
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+ "Malformed spread rules, no fields could be found",
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+ ));
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+ }
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+ Some(captures) => captures,
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+ };
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+
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+ let mut pattern = [false; 5];
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+ let pattern_vec: Vec<bool> = spread_rules_captures["pattern"]
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+ .chars()
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+ .map(|c| c == '#')
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+ .collect();
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+ pattern.copy_from_slice(&pattern_vec);
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+ let result = &spread_rules_captures["result"] == "#";
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+ spread_rules.0.insert(pattern, result);
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+ }
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+
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+ Ok(GrowthSimulation { pots, spread_rules, generations: 0 })
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+ }
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+}
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+
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+impl GrowthSimulation {
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+ fn advance_generation(&mut self) {
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+ let mut next_generation = VecDeque::new();
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+ let padding = &[false; 4];
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+ let pots_slice = self.pots.0.as_slices();
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+ let pots_slice = [padding, pots_slice.0, pots_slice.1, padding].concat();
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+ for (index, pot_window) in pots_slice.windows(5).enumerate() {
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+ match self.spread_rules.0.get(pot_window) {
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+ Some(result) => {
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+ next_generation.push_back(*result);
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+ },
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+ None => {
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+ next_generation.push_back(pots_slice[2]);
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+ },
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+ }
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+ }
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+ self.pots = Pots(next_generation);
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+ self.generations += 1;
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+ }
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+
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+ fn sum_plant_indices(&self) -> i32 {
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+ let mut sum: i32 = 0;
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+ for (index, pot) in self.pots.0.iter().enumerate() {
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+ if *pot {
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+ let shifted_index = index as i32 - self.generations as i32 * 2;
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+ sum += shifted_index;
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+ }
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+ }
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+ sum
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+ }
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+}
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+
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+fn read_initial_state_and_rules(filename: &str) -> Result<GrowthSimulation> {
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+ let input = fs::read_to_string(filename)?;
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+ Ok(input.parse()?)
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+}
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+
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+pub fn solve_part1() -> Result<i32> {
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+ let mut growth_sim = read_initial_state_and_rules(INPUT)?;
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+ for _ in 0..20 {
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+ growth_sim.advance_generation();
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+ }
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+ Ok(growth_sim.sum_plant_indices())
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+}
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+
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+pub fn solve_part2() -> Result<i32> {
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+ let mut growth_sim = read_initial_state_and_rules(INPUT)?;
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+ for _ in 0..50_000_000_000_i64 {
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+ growth_sim.advance_generation();
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+ }
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+ Ok(growth_sim.sum_plant_indices())
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+}
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+
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+#[cfg(test)]
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+mod tests {
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+ use super::*;
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+
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+ const TEST_INPUT: &str = "inputs/12_test.txt";
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+ fn test_growth_sim() -> GrowthSimulation {
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+ GrowthSimulation {
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+ pots: Pots(VecDeque::from(vec![
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+ true, false, false, true, false, true, false, false, true, true, false, false,
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+ false, false, false, false, true, true, true, false, false, false, true, true,
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+ true,
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+ ])),
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+ spread_rules: SpreadRules([
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+ ([true, true, true, true, false], true),
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+ ([true, true, false, true, true], true),
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+ ([false, false, true, false, false], true),
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+ ([false, true, false, false, false], true),
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+ ([true, true, false, true, false], true),
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+ ([false, true, true, true, true], true),
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+ ([true, false, true, true, true], true),
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+ ([true, true, true, false, true], true),
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+ ([false, true, false, true, true], true),
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+ ([true, false, true, false, true], true),
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+ ([false, true, false, true, false], true),
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+ ([false, true, true, false, false], true),
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+ ([true, true, true, false, false], true),
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+ ([false, false, false, true, true], true),
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+ ]
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+ .iter()
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+ .cloned()
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+ .collect()),
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+ generations: 0,
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+ }
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+ }
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+
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+ #[test]
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+ fn reads_initial_state_and_rules_file() {
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+ let growth_sim = read_initial_state_and_rules(TEST_INPUT).unwrap();
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+ assert_eq!(growth_sim, test_growth_sim());
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+ }
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+
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+ #[test]
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+ fn displays_growth_simulation() {
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+ assert_eq!(
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+ format!("{}", test_growth_sim()).lines().collect::<Vec<&str>>().sort(),
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+ vec![
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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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+ "##.#. => #",
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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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+ ".##.. => #",
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+ "###.. => #",
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+ "...## => #",
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+ ].sort()
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+ );
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+ }
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+
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+ #[test]
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+ fn advances_simulation_by_one_generation() {
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+ let mut growth_sim = test_growth_sim();
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+ growth_sim.advance_generation();
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+ assert_eq!(format!("{}", growth_sim.pots), "..#...#....#.....#..#..#..#..\n");
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+ }
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+
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+ #[test]
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+ fn returns_correct_sum_after_20_generations() {
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+ let mut growth_sim = test_growth_sim();
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+ for _ in 0..20 {
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+ growth_sim.advance_generation();
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+ }
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+ assert_eq!(growth_sim.sum_plant_indices(), 325);
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+ }
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+}
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