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2020: day22: use Hasher for part 2

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This commit is contained in:
Antoine Martin 2020-12-22 15:19:57 +01:00
parent 2ddd6b2bfc
commit 002f1a2b04
1 changed files with 10 additions and 3 deletions
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13
aoc2020/src/day22.rs
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@ -1,6 +1,8 @@
use std::cmp::Ordering; use std::cmp::Ordering;
use std::collections::hash_map::DefaultHasher;
use std::collections::{HashSet, VecDeque}; use std::collections::{HashSet, VecDeque};
use std::fmt::Write; use std::fmt::Write;
use std::hash::{Hash, Hasher};
use anyhow::{Context, Result}; use anyhow::{Context, Result};
@ -48,9 +50,14 @@ fn play_recursive_game(mut deck_a: Deck, mut deck_b: Deck) -> (Deck, bool) {
// exactly the same cards in the same order in the same players' decks, the game instantly // exactly the same cards in the same order in the same players' decks, the game instantly
// ends in a win for player 1. Previous rounds from other games are not considered. (This // ends in a win for player 1. Previous rounds from other games are not considered. (This
// prevents infinite games of Recursive Combat, which everyone agrees is a bad idea.) // prevents infinite games of Recursive Combat, which everyone agrees is a bad idea.)
let score_a = deck_score(&deck_a);
let score_b = deck_score(&deck_b); // we could use the score here, and it works on my input, but to be on the safe side let's
let hash = score_a * 100_000 + score_b; // just compute the hash manually (the goal is to avoid cloning entire Decks just to check
// their presence in the set)
let mut hasher = DefaultHasher::new();
deck_a.hash(&mut hasher);
deck_b.hash(&mut hasher);
let hash = hasher.finish();
if seen.contains(&hash) { if seen.contains(&hash) {
return (deck_a, true); return (deck_a, true);
} else { } else {