day_19 part_2

src/day_19/part_2/dummy_input.txt

@@ -0,0 +1,10 @@
+r, wr, b, g, bwu, rb, gb, br
+
+brwrr
+bggr
+gbbr
+rrbgbr
+ubwu
+bwurrg
+brgr
+bbrgwb

src/day_19/part_2/mod.rs

@@ -0,0 +1,42 @@
+use std::collections::HashMap;
+
+use itertools::Itertools;
+
+use super::parse;
+
+#[cfg(test)]
+mod test;
+
+fn num_compositions<'a>(
+    available: &Vec<&'a str>,
+    desired: &'a str,
+    compositions: &mut HashMap<(&'a str, &'a str), usize>,
+) -> usize {
+    available
+        .iter()
+        .map(move |towel| {
+            let key = (desired, *towel);
+            if compositions.contains_key(&key) {
+                *compositions.get(&key).unwrap()
+            } else {
+                let value = if *towel == desired {
+                    1
+                } else if desired.starts_with(towel) {
+                    num_compositions(available, desired[towel.len()..].as_ref(), compositions)
+                } else {
+                    0
+                };
+                compositions.insert(key, value);
+                value
+            }
+        })
+        .sum()
+}
+
+pub fn solve(input: &str) -> usize {
+    let (available, desired) = parse(input);
+    desired
+        .iter()
+        .map(|desired| num_compositions(&available, desired, &mut HashMap::<_, _>::new()))
+        .sum()
+}

src/day_19/part_2/test.rs

@@ -0,0 +1,16 @@
+use super::solve;
+use crate::include_using_path;
+
+#[test]
+fn dummy_input() {
+    let input = include_using_path!("dummy_input.txt");
+    let result = solve(input);
+    assert_eq!(result, 16);
+}
+
+#[test]
+fn solve_puzzle() {
+    let input = include_using_path!("input.txt");
+    let result = solve(input);
+    println!("Result: {}", result);
+}