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extern crate advent_of_code_2018;
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"))?;
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())
}
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