precompute word lettersets

src/main.rs

@@ -9,10 +9,14 @@ use crate::letterset::LetterSet;
 mod letterset;
 
 fn main() {
-    let dictionary: Vec<String> = BufReader::new(io::stdin().lock())
+    let dictionary: Vec<_> = BufReader::new(io::stdin().lock())
         .lines()
-        .collect::<Result<_, _>>()
-        .unwrap();
+        .map(|line| {
+            let word = line.unwrap();
+            let ls = LetterSet::from(&word);
+            (word, ls)
+        })
+        .collect();
 
     println!(
         "{:#?}",
@@ -23,7 +27,7 @@ fn main() {
     );
 }
 
-fn solve(dictionary: &[String], target: LetterSet) -> Option<(u16, Vec<String>)> {
+fn solve(dictionary: &[(String, LetterSet)], target: LetterSet) -> Option<(u16, Vec<String>)> {
     let mut bests = HashMap::new();
     bests.insert(LetterSet::EMPTY, (0, Vec::new()));
 
@@ -35,7 +39,7 @@ fn solve(dictionary: &[String], target: LetterSet) -> Option<(u16, Vec<String>)>
 // length doesn't include spaces. i think that's okay
 // assumes that `bests[LetterSet::EMPTY] == (0, Vec::new())`
 fn score(
-    dictionary: &[String],
+    dictionary: &[(String, LetterSet)],
     bests: &mut HashMap<LetterSet, (u16, Vec<String>)>,
     remaining: LetterSet,
 ) -> u16 {
@@ -43,25 +47,30 @@ fn score(
         return min.0;
     }
 
-    let Some((word, score)) = dictionary
+    let Some((word, ls, score)) = dictionary
         .iter()
-        .filter(|word| remaining != remaining.difference(LetterSet::from(word)))
-        .map(|word| {
+        .filter(|(_, ls)| !remaining.intersection(*ls).is_empty())
+        .map(|(word, ls)| {
             (
                 word,
+                ls,
                 (u16::try_from(word.len()).unwrap()).saturating_add(score(
                     dictionary,
                     bests,
-                    remaining.difference(LetterSet::from(word)),
+                    remaining.difference(*ls),
                 )),
             )
         })
-        .min_by_key(|(_, score)| *score)
+        .min_by_key(|(_, _, score)| *score)
     else {
         return u16::MAX;
     };
 
-    let remaining_after_word = remaining.difference(LetterSet::from(word));
+    if score == u16::MAX {
+        return score;
+    }
+
+    let remaining_after_word = remaining.difference(*ls);
     let (_score, path) = bests
         .get(&remaining_after_word)
         .expect("we already inserted this");