157 lines
4.3 KiB
Rust
157 lines
4.3 KiB
Rust
use std::collections::HashMap;
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use std::mem;
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fn parse_valve(line: &str) -> (&str, u32, Vec<&str>) {
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let (name, rest) = line
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.strip_prefix("Valve ")
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.unwrap()
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.split_once(" has flow rate=")
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.unwrap();
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let (rate, rest) = rest.split_once("; ").unwrap();
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let next = rest
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.strip_prefix("tunnel leads to valve ")
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.or_else(|| rest.strip_prefix("tunnels lead to valves "))
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.unwrap()
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.split(", ")
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.collect::<Vec<_>>();
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(name, rate.parse().unwrap(), next)
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}
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#[derive(Debug)]
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struct Valve {
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rate: u32,
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next: Vec<usize>,
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}
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fn prepare_valves<'a>(
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mut valves: Vec<(&'a str, u32, Vec<&str>)>,
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) -> (HashMap<&'a str, usize>, Vec<Valve>) {
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// All valves with a nonzero rate should come before the ones with a rate of
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// zero. This will help with our valve bitset later.
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valves.sort_by_key(|(_, rate, _)| *rate);
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valves.reverse();
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let names = valves
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.iter()
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.enumerate()
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.map(|(i, (n, _, _))| (*n, i))
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.collect::<HashMap<_, _>>();
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let valves = valves
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.into_iter()
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.map(|(_, rate, next)| {
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let next = next.into_iter().map(|n| names[n]).collect();
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Valve { rate, next }
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})
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.collect::<Vec<_>>();
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(names, valves)
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}
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#[derive(Debug, Clone, Copy, PartialEq, Eq, Hash)]
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struct OpenSet(u64);
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impl OpenSet {
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const ALL_CLOSED: Self = Self(0);
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/// The powerset of the set of all open valves.
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fn powerset(valves: &[Valve]) -> Vec<Self> {
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assert!(valves.len() <= 63);
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let first_zero_rate = valves
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.iter()
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.position(|v| v.rate == 0)
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.unwrap_or(valves.len());
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let until = 2_u64.pow(first_zero_rate as u32);
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(0..until).map(Self).collect::<Vec<_>>()
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}
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fn is_open(&self, valve_id: usize) -> bool {
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assert!(valve_id < 63);
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self.0 & (1 << valve_id) != 0
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}
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fn open(&self, valve_id: usize) -> Self {
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assert!(valve_id < 63);
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Self(self.0 | (1 << valve_id))
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}
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}
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#[derive(Debug)]
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struct Dp1 {
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valves: usize,
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powers: usize,
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elems: Vec<u32>,
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}
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impl Dp1 {
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fn new(valves: &[Valve], powerset: &[OpenSet]) -> Self {
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let valves = valves.len();
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let powers = powerset.len();
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let elems = vec![0; valves * powers];
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Self {
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valves,
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powers,
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elems,
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}
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}
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fn get(&self, valve_id: usize, open: OpenSet) -> u32 {
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self.elems[self.powers * valve_id + open.0 as usize]
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}
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fn set(&mut self, valve_id: usize, open: OpenSet, score: u32) {
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self.elems[self.powers * valve_id + open.0 as usize] = score;
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}
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fn clear(&mut self) {
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self.elems.fill(0);
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}
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}
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pub fn solve(input: String) {
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let valves = input.lines().map(parse_valve).collect::<Vec<_>>();
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let (names, valves) = prepare_valves(valves);
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let powerset = OpenSet::powerset(&valves);
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eprintln!("Powerset has size {}", powerset.len());
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// DP state consists of:
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// - The current minute
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// - The current valve
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// - The current set of open/closed valves
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let mut prev = Dp1::new(&valves, &powerset);
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let mut curr = Dp1::new(&valves, &powerset);
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// Given valve v in minute t with set s, you can either...
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// - Go to another neighbouring valve v', points: points[v', t-1, s]
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// - If v not in s: Open current valve, points: points[v, t-1, s+{v}] + t
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for minute in 1..=30 {
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eprintln!("Minute {minute}");
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mem::swap(&mut curr, &mut prev);
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curr.clear();
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for (valve_id, valve) in valves.iter().enumerate() {
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for open in &powerset {
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let mut score = valve
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.next
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.iter()
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.map(|next_id| prev.get(*next_id, *open))
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.max()
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.unwrap_or(0);
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if valve.rate > 0 && !open.is_open(valve_id) {
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let room_but_valve_open = prev.get(valve_id, open.open(valve_id));
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let pressure_until_end = (minute - 1) * valve.rate;
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score = score.max(room_but_valve_open + pressure_until_end);
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}
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curr.set(valve_id, *open, score);
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}
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}
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}
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let part1 = curr.get(names["AA"], OpenSet::ALL_CLOSED);
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println!("Part 1: {part1}");
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}
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