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Day 12 Complete. Thanks Reddit. The cache was a godsend!

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This commit is contained in:
Luke Else 2023-12-12 21:12:35 +00:00
parent 23b27a2a8a
commit f287d5a7ee
1 changed files with 40 additions and 11 deletions
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51
src/solutions/day12.rs
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@ -1,3 +1,5 @@
use std::collections::HashMap;
use super::Solution;
pub struct Day12 {}
@ -18,7 +20,7 @@ impl Solution for Day12 {
.map(|n| n.parse::<usize>().unwrap())
.collect::<Vec<_>>();
ans += self.solve(&springs.as_bytes(), None, &nums);
ans += self.solve(&springs.as_bytes(), None, &nums, &mut HashMap::new());
}
Ok(Box::new(ans))
}
@ -43,7 +45,7 @@ impl Solution for Day12 {
.map(|n| n.parse::<usize>().unwrap())
.collect::<Vec<_>>();
ans += self.solve(&springs.as_bytes(), None, &nums);
ans += self.solve(&springs.as_bytes(), None, &nums, &mut HashMap::new());
}
Ok(Box::new(ans))
}
@ -56,7 +58,13 @@ impl Solution for Day12 {
impl Day12 {
/// recursively counts the number of permutations of spring we could get from
/// the splits specified in 'nums'
fn solve(&self, s: &[u8], in_group: Option<usize>, cons: &[usize]) -> usize {
fn solve<'a, 'b>(
&self,
s: &'a [u8],
in_group: Option<usize>,
cons: &'b [usize],
map: &mut HashMap<(&'a [u8], Option<usize>, &'b [usize]), usize>,
) -> usize {
if s.is_empty() {
return match in_group {
Some(n) if cons == &[n] => 1,
@ -64,15 +72,36 @@ impl Day12 {
_ => 0,
};
}
// Resursively match based on the whether we are in a block and/or we have spaces left to fill
match (s[0], in_group, cons) {
(b'.', None, _) | (b'?', None, []) => self.solve(&s[1..], None, cons),
(b'.' | b'?', Some(n), [e, ..]) if n == *e => self.solve(&s[1..], None, &cons[1..]),
(b'#' | b'?', Some(n), [e, ..]) if n < *e => self.solve(&s[1..], Some(n + 1), cons),
(b'#', None, [_, ..]) => self.solve(&s[1..], Some(1), cons),
(b'?', None, _) => self.solve(&s[1..], None, cons) + self.solve(&s[1..], Some(1), cons),
_ => 0,
// Check for a cache hit
if s[0] == b'?' {
if let Some(result) = map.get(&(s, in_group, cons)) {
return *result;
}
}
// Resursively match based on the whether we are in a block and/or we have spaces left to fill
let ans = match (s[0], in_group, cons) {
(b'.', None, _) | (b'?', None, []) => self.solve(&s[1..], None, cons, map),
(b'.' | b'?', Some(n), [e, ..]) if n == *e => {
self.solve(&s[1..], None, &cons[1..], map)
}
(b'#' | b'?', Some(n), [e, ..]) if n < *e => {
self.solve(&s[1..], Some(n + 1), cons, map)
}
(b'#', None, [_, ..]) => self.solve(&s[1..], Some(1), cons, map),
(b'?', None, _) => {
self.solve(&s[1..], None, cons, map) + self.solve(&s[1..], Some(1), cons, map)
}
_ => 0,
};
// Store in cache
if s[0] == b'?' {
map.insert((s, in_group, cons), ans);
}
ans
}
}