diff options
Diffstat (limited to 'src/bin/day_24.rs')
| -rw-r--r-- | src/bin/day_24.rs | 203 |
1 files changed, 201 insertions, 2 deletions
diff --git a/src/bin/day_24.rs b/src/bin/day_24.rs index 0053f3d..d52f7d0 100644 --- a/src/bin/day_24.rs +++ b/src/bin/day_24.rs @@ -3,16 +3,215 @@ use advent_of_code_2018::*; use std::error::Error; use std::path::PathBuf; +use std::str::FromStr; + +use std::collections::HashMap; // cargo watch -cs "cargo run --release --bin day_24" +#[derive(Debug, Clone)] +struct Army { + units: u32, + hp: u32, + weaknesses: Vec<String>, + immunities: Vec<String>, + damage_type: String, + damage: u32, + initiative: u32 +} + +impl Army { + fn effective_power(&self) -> u32 { + self.units * self.damage + } + + fn actual_damage(&self, other: &Army) -> u32 { + let modifier = if other.weaknesses.contains(&self.damage_type) { + 2 + } else if other.immunities.contains(&self.damage_type) { + 0 + } else { + 1 + }; + self.effective_power() * modifier + } +} + +impl FromStr for Army { + type Err = Box<Error>; + + fn from_str(s: &str) -> Result<Self, Self::Err> { + // 2991 units each with 8084 hit points (weak to fire) with an attack that does 19 radiation damage at initiative 11 + let mut words = s.split_whitespace(); + let units = words.next().unwrap().parse()?; + let hp = words.nth(3).unwrap().parse()?; + let _ = words.nth(1); + + let mut weaknesses = Vec::new(); + let mut immunities = Vec::new(); + + let mut bracket_handled = false; + while !bracket_handled { + let maybe_weak_or_immune = words.next().unwrap().trim_matches(|c: char| !c.is_alphabetic()); + if maybe_weak_or_immune == "weak" { + let mut weakness = words.nth(1).unwrap(); + weaknesses.push(weakness.trim_matches(|c: char| !c.is_alphabetic()).to_string()); + while weakness.ends_with(',') { + weakness = words.next().unwrap(); + weaknesses.push(weakness.trim_matches(|c: char| !c.is_alphabetic()).to_string()); + } + } + else if maybe_weak_or_immune == "immune" { + let mut immunity = words.nth(1).unwrap(); + immunities.push(immunity.trim_matches(|c: char| !c.is_alphabetic()).to_string()); + while immunity.ends_with(',') { + immunity = words.next().unwrap(); + immunities.push(immunity.trim_matches(|c: char| !c.is_alphabetic()).to_string()); + } + } + else { + bracket_handled = true; + } + } + let damage = words.nth(4).unwrap().parse()?; + let damage_type = words.next().unwrap().to_string(); + let initiative = words.nth(3).unwrap().parse()?; + + Ok(Army { + units, hp, weaknesses, immunities, damage_type, damage, initiative + }) + } +} + + + fn main() -> Result<(), Box<Error>> { let input = read_file(&PathBuf::from("inputs/24.txt"))?; - println!("Input: {:?}", input); - + let mut input_iter = input.iter(); + let _ = input_iter.next(); + let immune_army: Vec<Army> = input_iter.by_ref() + .take_while(|&line| line != "Infection:") + .map(|line| line.parse().unwrap()) + .collect(); + let infection_army: Vec<Army> = input_iter + .map(|line| line.parse().unwrap()) + .collect(); + let (unboosted_immune_army_size, unboosted_infection_army_size) = simulate(&immune_army, &infection_army, 0); + debug!(unboosted_immune_army_size); + debug!(unboosted_infection_army_size); + for boost in 0.. { + debug!(boost); + let (immune_army_size, infection_army_size) = simulate(&immune_army, &infection_army, boost); + debug!(immune_army_size); + debug!(infection_army_size); + if immune_army_size > 0 { + break; + } + } Ok(()) } + + +fn target_selection(targeting_army: &Vec<Army>, targeted_army: &Vec<Army>) -> HashMap<usize, usize> { + let mut targets = HashMap::new(); + for (i, army) in targeting_army.iter().enumerate() { + let best_target = (0..targeted_army.len()) + .filter(|potential_target| !targets.values().any(|targeted| targeted == potential_target)) + .fold(None, |best_target, next| { + let next_actual_damage = army.actual_damage(&targeted_army[next]); + let last_best_actual_damage = best_target.map(|best_target| army.actual_damage(&targeted_army[best_target])).unwrap_or(0); + let next_effective_power = targeted_army[next].effective_power(); + let last_best_effective_power = best_target.map(|best_target: usize| targeted_army[best_target].effective_power()).unwrap_or(0); + let next_initiative = targeted_army[next].initiative; + let last_best_initiative = best_target.map(|best_target| targeted_army[best_target].initiative).unwrap_or(0); + if next_actual_damage == 0 && last_best_actual_damage == 0 { + None + } else if next_actual_damage > last_best_actual_damage { + Some(next) + } else if next_actual_damage == last_best_actual_damage && next_effective_power > last_best_effective_power { + Some(next) + } else if next_actual_damage == last_best_actual_damage && next_effective_power == last_best_effective_power && next_initiative > last_best_initiative { + Some(next) + } else { + best_target + } + }); + + if let Some(best_target) = best_target { + targets.insert(i, best_target); + } + } + + targets +} + +fn attack(aggressor: &Army, target: &mut Army) { + let damage = aggressor.actual_damage(target); + let units_destroyed = damage / target.hp; + target.units = target.units.saturating_sub(units_destroyed); +} + + +fn simulate(immune_army: &[Army], infection_army: &[Army], boost: u32) -> (u32, u32) { + let mut infection_army = Vec::from(infection_army); + + let mut immune_army: Vec<Army> = immune_army.iter().map(|army| Army { + damage: army.damage + boost, + ..army.clone() + }).collect(); + + let mut watchdog_sum = immune_army.iter().map(|a| a.units).sum::<u32>() + infection_army.iter().map(|a| a.units).sum::<u32>(); + while immune_army.len() > 0 && infection_army.len() > 0 { + immune_army.sort_by(|a, b| b.effective_power().cmp(&a.effective_power()).then(b.initiative.cmp(&a.initiative))); + infection_army.sort_by(|a, b| b.effective_power().cmp(&a.effective_power()).then(b.initiative.cmp(&a.initiative))); + + let mut immune_targets = target_selection(&immune_army, &infection_army); + let mut infection_targets = target_selection(&infection_army, &immune_army); + + while immune_targets.len() > 0 || infection_targets.len() > 0 { + let next_immune = immune_targets.keys() + .map(|&k| (k, immune_army[k].initiative.clone())) + .max_by_key(|(_, initiative)| *initiative); + let next_infection = infection_targets.keys() + .map(|&k| (k, infection_army[k].initiative.clone())) + .max_by_key(|(_, initiative)| *initiative); + match (next_immune, next_infection) { + (None, None) => { + panic!("No targets left") + }, + (Some((immune_key, immune_init)), Some((_infect_key, infect_init))) if immune_init > infect_init => { + attack(&immune_army[immune_key], &mut infection_army[*immune_targets.get(&immune_key).unwrap()]); + immune_targets.remove(&immune_key); + }, + (Some((_immune_key, _immune_init)), Some((infect_key, _infect_init))) => { + attack(&infection_army[infect_key], &mut immune_army[*infection_targets.get(&infect_key).unwrap()]); + infection_targets.remove(&infect_key); + }, + (Some((immune_key, _immune_init)), None) => { + attack(&immune_army[immune_key], &mut infection_army[*immune_targets.get(&immune_key).unwrap()]); + immune_targets.remove(&immune_key); + }, + (None, Some((infect_key, _infect_init))) => { + attack(&infection_army[infect_key], &mut immune_army[*infection_targets.get(&infect_key).unwrap()]); + infection_targets.remove(&infect_key); + } + }; + } + + immune_army.retain(|a| a.units > 0); + infection_army.retain(|a| a.units > 0); + + let new_watchdog_sum = immune_army.iter().map(|a| a.units).sum::<u32>() + infection_army.iter().map(|a| a.units).sum::<u32>(); + if watchdog_sum == new_watchdog_sum { + // Stalemate! Everyone loses. + return (0, 0); + } + watchdog_sum = new_watchdog_sum; + } + + (immune_army.iter().map(|a| a.units).sum(), infection_army.iter().map(|a| a.units).sum()) +} |