19th day

Author: majcn

Diff for: data/examples/19.txt

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

Diff for: src/bin/19.rs

@@ -0,0 +1,88 @@
+advent_of_code::solution!(19);
+
+use advent_of_code::maneatingape::hash::*;
+
+fn parse_data(input: &str) -> (Vec<&str>, Vec<&str>) {
+    let (left, right) = input.split_once("\n\n").unwrap();
+
+    let towels = left.split(", ").collect();
+    let messages = right.lines().collect();
+
+    (towels, messages)
+}
+
+fn validate_message(message: &str, towels: &[&str]) -> bool {
+    if message.is_empty() {
+        return true;
+    }
+
+    towels
+        .iter()
+        .filter(|towel| message.len() >= towel.len())
+        .filter(|towel| &&&message[..towel.len()] == towel)
+        .any(|towel| validate_message(&message[towel.len()..], towels))
+}
+
+fn count_valid_message(cache: &mut FastMap<String, u64>, message: &str, towels: &[&str]) -> u64 {
+    if message.is_empty() {
+        return 1;
+    }
+
+    if let Some(&result) = cache.get(message) {
+        return result;
+    }
+
+    towels
+        .iter()
+        .filter(|towel| message.len() >= towel.len())
+        .filter(|towel| &&&message[..towel.len()] == towel)
+        .map(|towel| {
+            let result = count_valid_message(cache, &message[towel.len()..], towels);
+            cache.insert(String::from(&message[towel.len()..]), result);
+            result
+        })
+        .sum()
+}
+
+pub fn part_one(input: &str) -> Option<u32> {
+    let (towels, messages) = parse_data(input);
+
+    let result = messages
+        .into_iter()
+        .filter(|message| validate_message(message, &towels))
+        .count() as u32;
+
+    Some(result)
+}
+
+pub fn part_two(input: &str) -> Option<u64> {
+    let (towels, messages) = parse_data(input);
+
+    let mut cache = FastMap::new();
+
+    let result = messages
+        .into_iter()
+        .map(|message| count_valid_message(&mut cache, message, &towels))
+        .sum();
+
+    Some(result)
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+
+    #[test]
+    fn test_part_one() {
+        let input = advent_of_code::template::read_file("examples", DAY);
+        let result = part_one(&input);
+        assert_eq!(result, Some(6));
+    }
+
+    #[test]
+    fn test_part_two() {
+        let intput = advent_of_code::template::read_file("examples", DAY);
+        let result = part_two(&intput);
+        assert_eq!(result, Some(16));
+    }
+}