solution: day 19

data/examples/19.txt

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

src/bin/19.rs

@@ -0,0 +1,71 @@
+use hashbrown::{HashMap, HashSet};
+
+fn parse_input(input: &str) -> (HashSet<&str>, HashSet<&str>) {
+    let (upatterns, udesigns) = input.split_once("\n\n").unwrap();
+
+    let patterns = upatterns.split(", ").collect();
+    let designs = udesigns.split('\n').collect();
+
+    (patterns, designs)
+}
+
+fn count_pattern_designs<'a>(
+    memo: &mut HashMap<&'a str, usize>,
+    patterns: &HashSet<&str>,
+    pattern: &'a str,
+) -> usize {
+    if pattern.is_empty() {
+        return 1;
+    }
+
+    if !memo.contains_key(pattern) {
+        let mut count = 0;
+        for p in patterns.iter() {
+            if let Some(stripped) = pattern.strip_prefix(p) {
+                count += count_pattern_designs(memo, patterns, stripped)
+            }
+        }
+        memo.insert(pattern, count);
+    }
+
+    memo[pattern]
+}
+
+pub fn part_one(input: &str) -> Option<usize> {
+    let (patterns, designs) = parse_input(input);
+
+    let mut memo = HashMap::new();
+
+    for d in designs.iter().copied() {
+        count_pattern_designs(&mut memo, &patterns, d);
+    }
+
+    designs.into_iter().filter(|x| memo[x] > 0).count().into()
+}
+
+pub fn part_two(input: &str) -> Option<usize> {
+    let (patterns, designs) = parse_input(input);
+
+    let mut memo = HashMap::new();
+
+    for d in designs.iter().copied() {
+        count_pattern_designs(&mut memo, &patterns, d);
+    }
+
+    designs.into_iter().map(|x| memo[x]).sum::<usize>().into()
+}
+
+aoc::solution!(19);
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    #[test]
+    fn test_part_one() {
+        assert_eq!(part_one(&aoc::template::read_file("examples", 19)), Some(6));
+    }
+    #[test]
+    fn test_part_two() {
+        assert_eq!(part_two(&aoc::template::read_file("examples", 19)), Some(16));
+    }
+}