dramatically less cloning

.gitignore

@@ -1 +1,4 @@
 /target
+perf.data
+perf.data.old
+flamegraph.svg

Cargo.toml

@@ -4,3 +4,6 @@ version = "0.1.0"
 edition = "2024"
 
 [dependencies]
+
+[profile.release]
+debug = true

src/main.rs

@@ -1,5 +1,6 @@
 use std::{
     collections::HashMap,
+    env,
     io::{self, BufRead, BufReader},
 };
 
@@ -13,43 +14,63 @@ fn main() {
         .collect::<Result<_, _>>()
         .unwrap();
 
+    println!(
+        "{:#?}",
+        solve(
+            &dictionary,
+            LetterSet::from(
+                env::args()
+                    .nth(1)
+                    .expect("give me the letters you want NOW")
+            )
+        )
+    );
+}
+
+fn solve(dictionary: &[String], target: LetterSet) -> Option<(u16, Vec<String>)> {
     let mut bests = HashMap::new();
-    let best = solve(dictionary.as_slice(), &mut bests, LetterSet::FULL);
-    println!("{best:?}");
+    bests.insert(LetterSet::EMPTY, (0, Vec::new()));
+
+    score(dictionary, &mut bests, target);
+
+    bests.get(&target).cloned()
 }
 
 // length doesn't include spaces. i think that's okay
-fn solve(
+// assumes that `bests[LetterSet::EMPTY] == (0, Vec::new())`
+fn score(
     dictionary: &[String],
     bests: &mut HashMap<LetterSet, (u16, Vec<String>)>,
     remaining: LetterSet,
-) -> (u16, Vec<String>) {
-    if remaining.is_empty() {
-        return (0, Vec::new());
-    }
-
+) -> u16 {
     if let Some(min) = bests.get(&remaining) {
-        return min.clone();
+        return min.0;
     }
 
-    let best = dictionary
+    let Some((word, score)) = dictionary
         .iter()
-        .filter(|word| remaining != remaining.difference(LetterSet::from(word.as_bytes())))
+        .filter(|word| remaining != remaining.difference(LetterSet::from(word)))
         .map(|word| {
-            let (score, mut path) = solve(
+            (
+                word,
+                (u16::try_from(word.len()).unwrap()).saturating_add(score(
                     dictionary,
                     bests,
                     remaining.difference(LetterSet::from(word)),
-            );
-            path.push(word.clone());
-            (
-                (u16::try_from(word.len()).unwrap()).saturating_add(score),
-                path,
+                )),
             )
         })
-        .min()
-        .unwrap_or((u16::MAX, Vec::new()));
+        .min_by_key(|(_, score)| *score)
+    else {
+        return u16::MAX;
+    };
 
-    bests.insert(remaining, best.clone());
-    best
+    let remaining_after_word = remaining.difference(LetterSet::from(word));
+    let (_score, path) = bests
+        .get(&remaining_after_word)
+        .expect("we already inserted this");
+    let mut path = path.clone();
+    path.push(word.clone());
+    bests.insert(remaining, (score, path));
+    score
 }