[2024] Day 19 initial solution

Author: connorslade

README.md

@@ -23,6 +23,7 @@ Thank you to [Eric Wastl](http://was.tl) for running this incredible yearly even
 - [Day 16: Reindeer Maze](aoc_2024/src/day_16.rs)
 - [Day 17: Chronospatial Computer](aoc_2024/src/day_17.rs)
 - [Day 18: RAM Run](aoc_2024/src/day_18.rs)
+- [Day 19: Linen Layout](aoc_2024/src/day_19.rs)
 <!-- MARKER -->
 
 ## [2023](https://adventofcode.com/2023) [![aoc_2023](https://github.com/connorslade/advent-of-code/actions/workflows/aoc_2023.yml/badge.svg)](https://github.com/connorslade/advent-of-code/actions/workflows/aoc_2023.yml)

aoc_2024/src/day_19.rs

@@ -0,0 +1,132 @@
+use std::collections::HashMap;
+
+use common::{solution, Answer};
+
+solution!("Linen Layout", 19);
+
+fn part_a(input: &str) -> Answer {
+    let problem = Problem::parse(input);
+    let mut sum = 0;
+
+    for i in 0..problem.needed.len() {
+        if problem.possible(i) {
+            sum += 1;
+        }
+    }
+
+    sum.into()
+}
+
+fn part_b(input: &str) -> Answer {
+    let problem = Problem::parse(input);
+    let mut sum = 0;
+
+    for i in 0..problem.needed.len() {
+        sum += problem.ways(i);
+    }
+
+    sum.into()
+}
+
+struct Problem {
+    sources: Vec<String>,
+    needed: Vec<String>,
+}
+
+impl Problem {
+    fn parse(input: &str) -> Self {
+        let (sources, needed) = input.split_once("\n\n").unwrap();
+        let sources = sources.split(", ").map(|x| x.to_owned()).collect();
+        let needed = needed.lines().map(|x| x.to_owned()).collect();
+
+        Self { sources, needed }
+    }
+
+    fn possible(&self, design: usize) -> bool {
+        fn _inner<'a>(
+            memo: &mut HashMap<&'a str, bool>,
+            expected: &'a str,
+            sources: &[String],
+        ) -> bool {
+            if let Some(&cache) = memo.get(expected) {
+                return cache;
+            }
+
+            if expected.len() == 0 {
+                memo.insert(expected, true);
+                return true;
+            }
+
+            for source in sources {
+                if expected.len() >= source.len()
+                    && expected.starts_with(source)
+                    && _inner(memo, &expected[source.len()..], &sources)
+                {
+                    memo.insert(expected, true);
+                    return true;
+                }
+            }
+
+            memo.insert(expected, false);
+            false
+        }
+
+        _inner(&mut HashMap::new(), &self.needed[design], &self.sources)
+    }
+
+    fn ways(&self, design: usize) -> u64 {
+        fn _inner<'a>(
+            memo: &mut HashMap<&'a str, u64>,
+            expected: &'a str,
+            sources: &[String],
+        ) -> u64 {
+            if let Some(&cache) = memo.get(expected) {
+                return cache;
+            }
+
+            if expected.len() == 0 {
+                return 1;
+            }
+
+            let mut ways = 0;
+            for source in sources {
+                if expected.len() >= source.len() && expected.starts_with(source) {
+                    ways += _inner(memo, &expected[source.len()..], &sources);
+                }
+            }
+
+            memo.insert(expected, ways);
+            ways
+        }
+
+        _inner(&mut HashMap::new(), &self.needed[design], &self.sources)
+    }
+}
+
+#[cfg(test)]
+mod test {
+    use indoc::indoc;
+
+    const CASE: &str = indoc! {"
+        r, wr, b, g, bwu, rb, gb, br
+
+        brwrr
+        bggr
+        gbbr
+        rrbgbr
+        ubwu
+        bwurrg
+        brgr
+        bbrgwb
+    "};
+
+    #[test]
+    fn part_a() {
+        assert_eq!(super::part_a(CASE), 6.into());
+    }
+
+    #[test]
+    fn part_b() {
+        assert_eq!(super::part_b(CASE), 16.into());
+    }
+}

aoc_2024/src/lib.rs

@@ -18,6 +18,7 @@ mod day_15;
 mod day_16;
 mod day_17;
 mod day_18;
+mod day_19;
 // [import_marker]
 
 pub const SOLUTIONS: &[Solution] = &[
@@ -39,5 +40,6 @@ pub const SOLUTIONS: &[Solution] = &[
     day_16::SOLUTION,
     day_17::SOLUTION,
     day_18::SOLUTION,
+    day_19::SOLUTION,
     // [list_marker]
 ];