dramatically reduce memory usage

ACQUEST ADZ ALKY AMPING ARF AVOW BAH JEUX

src/main.rs

@@ -1,6 +1,4 @@
 use std::{
-    array,
-    collections::HashSet,
     env,
     io::{self, BufRead, BufReader},
     process,
@@ -22,25 +20,39 @@ fn main() {
 
     let target = env::args().nth(1).map_or(LetterSet::FULL, LetterSet::from);
     println!("letter count: {}", target.len());
-    let (len, path) = solve(&mut dictionary, target);
+    let Some((len, path)) = solve(&mut dictionary, target) else {
+        println!("failed :(");
+        process::exit(1);
+    };
     println!("{len}: {}", path.into_iter().collect::<Vec<_>>().join(" "));
 }
 
 const MAX_SOLUTION_LENGTH: u8 = 200;
 
-fn solve(dictionary: &mut [(String, LetterSet)], target: LetterSet) -> (u8, HashSet<String>) {
+fn solve(dictionary: &mut [(String, LetterSet)], target: LetterSet) -> Option<(u8, Vec<&str>)> {
     let mut bests = (0..=LetterSet::FULL.to_index())
-        .map(|_| (u8::MAX, HashSet::new()))
+        .map(|_| (u8::MAX, None))
         .collect::<Box<[_]>>();
     println!("allocated!");
-    bests[LetterSet::FULL.to_index()] = (0, HashSet::new());
+    bests[LetterSet::FULL.to_index()] = (0, None);
 
     dictionary.sort_by_key(|(word, ls)| word.len() - usize::from(ls.len()));
     println!("sorted!");
 
     score(dictionary, &mut bests, target.negation(), 0);
 
-    bests[target.negation().to_index()].clone()
+    let (len, start) = bests[target.negation().to_index()];
+    let start = start?;
+
+    let mut path = vec![start];
+    let mut done = LetterSet::from(start);
+
+    while let (_, Some(word)) = bests[done.to_index()] {
+        path.push(word);
+        done = done.union(LetterSet::from(word));
+    }
+
+    Some((len, path))
 }
 
 // TODO: perhaps bottom up? (pick or no pick) (real potential!) (not obvious how to do path)
@@ -48,9 +60,9 @@ fn solve(dictionary: &mut [(String, LetterSet)], target: LetterSet) -> (u8, Hash
 // length doesn't include spaces. i think that's okay
 // bests is sorta inverted; the keys are completed letters
 // assumes that `bests[LetterSet::FULL] == (0, Vec::new())`
-fn score(
+fn score<'d>(
-    dictionary: &[(String, LetterSet)],
+    dictionary: &'d [(String, LetterSet)],
-    bests: &mut [(u8, HashSet<String>)],
+    bests: &mut [(u8, Option<&'d str>)],
     done_letters: LetterSet,
     length: u8,
 ) -> u8 {
@@ -63,7 +75,7 @@ fn score(
         return known;
     }
 
-    let Some((word, ls, score)) = dictionary
+    let Some((word, score)) = dictionary
         .iter()
         .filter(|(word, ls)| {
             (!ls.difference(done_letters).is_empty())
@@ -73,16 +85,15 @@ fn score(
             let word_len = u8::try_from(word.len()).unwrap();
             let new_length = word_len.saturating_add(length);
             let rest_score = score(dictionary, bests, done_letters.union(*ls), new_length);
-            (word, ls, word_len.saturating_add(rest_score))
+            (word, word_len.saturating_add(rest_score))
         })
-        .take(2000)
+        .take(1000)
-        .min_by_key(|(_, _, score)| *score)
+        .min_by_key(|(_, score)| *score)
     else {
         return u8::MAX;
     };
 
     bests[done_letters.to_index()].0 = score;
-    bests[done_letters.to_index()].1 = bests[done_letters.union(*ls).to_index()].1.clone();
+    bests[done_letters.to_index()].1 = Some(word);
-    bests[done_letters.to_index()].1.insert(word.clone());
     score
 }