Rust/2024/19: improve solution

Author: Defelo

Rust/2024/19.rs

@@ -1,30 +1,34 @@
 #![feature(test)]
 
+use aoc::trie::Trie;
 use rayon::iter::{IntoParallelRefIterator, ParallelIterator};
 
 #[derive(Debug)]
 struct Input {
-    patterns: Vec<String>,
-    designs: Vec<String>,
+    patterns: Trie<u8>,
+    designs: Vec<Vec<u8>>,
 }
 
 fn setup(input: &str) -> Input {
     let mut lines = input.trim().lines();
-    let patterns = lines.next().unwrap().split(", ").map(Into::into).collect();
+    let patterns = lines
+        .next()
+        .unwrap()
+        .split(", ")
+        .map(|p| p.bytes())
+        .collect();
     let designs = lines.skip(1).map(Into::into).collect();
     Input { patterns, designs }
 }
 
-fn count(design: &str, patterns: &[String]) -> usize {
+fn count(design: &[u8], patterns: &Trie<u8>) -> usize {
     let mut dp = vec![0; design.len() + 1];
     dp[design.len()] = 1;
     for i in (0..design.len()).rev() {
-        for p in patterns {
-            if i + p.len() > design.len() || !design[i..].starts_with(p) {
-                continue;
-            }
-            dp[i] += dp[i + p.len()];
-        }
+        dp[i] = patterns
+            .prefix_matches(design[i..].iter().copied())
+            .map(|len| dp[i + len])
+            .sum();
     }
     dp[0]
 }

Rust/lib/lib.rs

@@ -10,6 +10,7 @@ pub mod iter_ext;
 pub mod math;
 pub mod parsing;
 pub mod range;
+pub mod trie;
 pub mod tuples;
 
 extern crate test;

Rust/lib/trie.rs

@@ -0,0 +1,132 @@
+use std::hash::Hash;
+
+use rustc_hash::FxHashMap;
+
+#[derive(Debug, Clone)]
+pub struct Trie<T>(Vec<TrieNode<T>>);
+
+#[derive(Debug, Clone)]
+struct TrieNode<T> {
+    flag: bool,
+    next: FxHashMap<T, usize>,
+}
+
+impl<T> Trie<T> {
+    pub fn new() -> Self {
+        Self::default()
+    }
+}
+
+impl<T: Eq + Hash> Trie<T> {
+    pub fn insert(&mut self, item: impl IntoIterator<Item = T>) -> bool {
+        let mut node = 0;
+        for x in item {
+            match self.0[node].next.get(&x) {
+                Some(&next) => node = next,
+                None => {
+                    let next = self.0.len();
+                    self.0.push(TrieNode::default());
+                    self.0[node].next.insert(x, next);
+                    node = next;
+                }
+            }
+        }
+        !std::mem::replace(&mut self.0[node].flag, true)
+    }
+
+    pub fn contains(&self, item: impl IntoIterator<Item = T>) -> bool {
+        let mut node = 0;
+        for x in item {
+            match self.0[node].next.get(&x) {
+                Some(&next) => node = next,
+                None => return false,
+            }
+        }
+        self.0[node].flag
+    }
+
+    pub fn prefix_matches<U: IntoIterator<Item = T>>(
+        &self,
+        item: U,
+    ) -> impl Iterator<Item = usize> + use<'_, T, U> {
+        self.0[0].flag.then_some(0).into_iter().chain(
+            item.into_iter()
+                .scan(0, |node, x| {
+                    self.0[*node].next.get(&x).map(|&next| {
+                        *node = next;
+                        self.0[*node].flag
+                    })
+                })
+                .enumerate()
+                .flat_map(|(i, flag)| flag.then_some(i + 1)),
+        )
+    }
+}
+
+impl<T> Default for Trie<T> {
+    fn default() -> Self {
+        Self(vec![TrieNode::default()])
+    }
+}
+
+impl<T> Default for TrieNode<T> {
+    fn default() -> Self {
+        Self {
+            flag: false,
+            next: Default::default(),
+        }
+    }
+}
+
+impl<I2> FromIterator<I2> for Trie<I2::Item>
+where
+    I2: IntoIterator,
+    I2::Item: Eq + Hash,
+{
+    fn from_iter<I1: IntoIterator<Item = I2>>(iter: I1) -> Self {
+        let mut trie = Self::new();
+        for item in iter {
+            trie.insert(item);
+        }
+        trie
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn trie() {
+        let mut t = ["foo", "bar", "baz"]
+            .into_iter()
+            .map(|x| x.chars())
+            .collect::<Trie<_>>();
+
+        assert!(t.contains("foo".chars()));
+        assert!(t.contains("bar".chars()));
+        assert!(t.contains("baz".chars()));
+        assert!(!t.contains("test".chars()));
+        assert!(!t.contains("baa".chars()));
+
+        assert!(t.insert("test".chars()));
+        assert!(t.contains("test".chars()));
+        assert!(!t.insert("test".chars()));
+        assert!(t.contains("test".chars()));
+    }
+
+    #[test]
+    fn prefix_matches() {
+        let t = ["", "123", "12345", "1234567", "test", "12xy"]
+            .into_iter()
+            .map(|x| x.chars())
+            .collect::<Trie<_>>();
+
+        assert_eq!(
+            t.prefix_matches("123456789".chars()).collect::<Vec<_>>(),
+            [0, 3, 5, 7]
+        );
+
+        assert_eq!(t.prefix_matches("".chars()).collect::<Vec<_>>(), [0]);
+    }
+}