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21/2 optimizations

This commit is contained in:
kageru 2021-12-22 00:41:17 +01:00
parent b262f734b5
commit b733d05353
Signed by: kageru
GPG Key ID: 8282A2BEA4ADA3D2
1 changed files with 11 additions and 7 deletions
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18
2021/src/bin/day21.rs
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@ -10,8 +10,8 @@ fn part1((p1, p2): Parsed) -> usize {
.cycle()
.skip(1)
.step_by(3)
.scan(GameState { odd_round: false, scores: [(p1, 0), (p2, 0)] }, |mut game, die| {
advance_game(&mut game, die * 3);
.scan(GameState { odd_round: false, scores: [(p1, 0), (p2, 0)] }, |game, die| {
advance_game(game, die * 3);
Some((game.scores[0].1, game.scores[1].1))
})
.zip(1..)
@ -31,23 +31,27 @@ struct GameState {
const POSSIBLE_ROLLS: [(u16, usize); 7] = [(6, 7), (5, 6), (7, 6), (4, 3), (8, 3), (3, 1), (9, 1)];
fn part2((p1, p2): Parsed) -> usize {
let start = GameState { odd_round: false, scores: [(p1, 0), (p2, 0)] };
let mut games = FnvHashMap::default();
games.insert(start, 1);
games.insert(GameState { odd_round: false, scores: [(p1, 0), (p2, 0)] }, 1);
let mut wins = [0, 0];
let mut storage = Vec::with_capacity(100_000);
while !games.is_empty() {
for k in games.clone().keys() {
let (start, count) = games.remove_entry(k).unwrap();
for (start, count) in games.drain() {
for &(die, count2) in &POSSIBLE_ROLLS {
let mut new_state = start;
advance_game(&mut new_state, die);
if new_state.scores[start.odd_round as usize].1 >= 21 {
wins[new_state.odd_round as usize] += count * count2;
} else {
*games.entry(new_state).or_insert(0) += count * count2;
storage.push((new_state, count * count2));
}
}
}
// Of all the versions I’ve tried, temporarily storing in a vector and then sorting back
// into the map was by far the fastest.
for (k, v) in storage.drain(..) {
*games.entry(k).or_insert(0) += v;
}
}
wins[0].max(wins[1])
}