day 19 part 2

src/day19.rs

@@ -0,0 +1,98 @@
+use std::{
+    collections::{HashMap, HashSet},
+    fs::read_to_string,
+};
+
+pub fn day_main() {
+    let input = read_to_string("input/day19.txt").unwrap();
+    let input = input.trim();
+    println!(" part1: {}", part1(input));
+    println!(" part2: {}", part2(input));
+}
+
+type RiddleResult = usize;
+
+fn part1(input: &str) -> RiddleResult {
+    let (a, b) = input.split_once("\n\n").unwrap();
+    let towels: HashSet<&str> = a.split(", ").collect();
+    b.lines().filter(|line| possible(line, &towels)).count()
+}
+
+fn possible(line: &str, towels: &HashSet<&str>) -> bool {
+    if line.is_empty() {
+        return true;
+    }
+    for t in towels.iter() {
+        if let Some(suffix) = line.strip_prefix(t) {
+            if possible(suffix, towels) {
+                return true;
+            }
+        }
+    }
+    false
+}
+
+fn countp<'a>(
+    line: &'a str,
+    towels: &HashSet<&str>,
+    solved: &mut HashMap<&'a str, usize>,
+) -> usize {
+    if line.is_empty() {
+        return 1;
+    }
+    if let Some(count) = solved.get(line) {
+        return *count;
+    }
+    let mut summed = 0;
+    for t in towels.iter() {
+        if let Some(suffix) = line.strip_prefix(t) {
+            summed += countp(suffix, towels, solved);
+        }
+    }
+    solved.insert(line, summed);
+    summed
+}
+fn part2(input: &str) -> RiddleResult {
+    let (a, b) = input.split_once("\n\n").unwrap();
+    let towels: HashSet<&str> = a.split(", ").collect();
+    b.lines()
+        .map(|line| countp(line, &towels, &mut HashMap::new()))
+        .sum()
+}
+
+#[cfg(test)]
+mod test {
+    use std::collections::HashSet;
+
+    use crate::day19::possible;
+
+    use super::{part1, part2};
+
+    const TEST_INPUT: &str = r"r, wr, b, g, bwu, rb, gb, br
+
+brwrr
+bggr
+gbbr
+rrbgbr
+ubwu
+bwurrg
+brgr
+bbrgwb
+";
+
+    #[test]
+    fn test1() {
+        assert_eq!(part1(TEST_INPUT), 6);
+    }
+
+    #[test]
+    fn solver() {
+        let set = HashSet::from_iter(["r", "wr", "b", "g", "bwu", "rb", "gb", "br"]);
+        assert!(possible("bwurrg", &set));
+    }
+
+    #[test]
+    fn test2() {
+        assert_eq!(part2(TEST_INPUT), 16);
+    }
+}

src/lib.rs

@@ -15,5 +15,6 @@ pub mod day14;
 pub mod day15;
 pub mod day16;
 pub mod day17;
+pub mod day19;
 // PLACEHOLDER
 pub mod utils;

src/main.rs

@@ -22,6 +22,7 @@ fn main() {
         (15, day15::day_main),
         (16, day16::day_main),
         (17, day17::day_main),
+        (19, day19::day_main),
         // PLACEHOLDER
     ]);
     let day: Option<u8> = args().nth(1).and_then(|a| a.parse().ok());